945=x(20+x)+3x+-30

Solution for 945=x(20+x)+3x+-30 equation:

Simplifying
945 = x(20 + x) + 3x + -30
945 = (20 * x + x * x) + 3x + -30
945 = (20x + x2) + 3x + -30

Reorder the terms:
945 = -30 + 20x + 3x + x2

Combine like terms: 20x + 3x = 23x
945 = -30 + 23x + x2

Solving
945 = -30 + 23x + x2

Solving for variable 'x'.

Combine like terms: 945 + 30 = 975
975 + -23x + -1x2 = -30 + 23x + x2 + 30 + -23x + -1x2

Reorder the terms:
975 + -23x + -1x2 = -30 + 30 + 23x + -23x + x2 + -1x2

Combine like terms: -30 + 30 = 0
975 + -23x + -1x2 = 0 + 23x + -23x + x2 + -1x2
975 + -23x + -1x2 = 23x + -23x + x2 + -1x2

Combine like terms: 23x + -23x = 0
975 + -23x + -1x2 = 0 + x2 + -1x2
975 + -23x + -1x2 = x2 + -1x2

Combine like terms: x2 + -1x2 = 0
975 + -23x + -1x2 = 0

Begin completing the square.  Divide all terms by
-1 the coefficient of the squared term: 

Divide each side by '-1'.
-975 + 23x + x2 = 0

Move the constant term to the right:

Add '975' to each side of the equation.
-975 + 23x + 975 + x2 = 0 + 975

Reorder the terms:
-975 + 975 + 23x + x2 = 0 + 975

Combine like terms: -975 + 975 = 0
0 + 23x + x2 = 0 + 975
23x + x2 = 0 + 975

Combine like terms: 0 + 975 = 975
23x + x2 = 975

The x term is 23x.  Take half its coefficient (11.5).
Square it (132.25) and add it to both sides.

Add '132.25' to each side of the equation.
23x + 132.25 + x2 = 975 + 132.25

Reorder the terms:
132.25 + 23x + x2 = 975 + 132.25

Combine like terms: 975 + 132.25 = 1107.25
132.25 + 23x + x2 = 1107.25

Factor a perfect square on the left side:
(x + 11.5)(x + 11.5) = 1107.25

Calculate the square root of the right side: 33.275366264

Break this problem into two subproblems by setting 
(x + 11.5) equal to 33.275366264 and -33.275366264.

Subproblem 1
x + 11.5 = 33.275366264

Simplifying
x + 11.5 = 33.275366264

Reorder the terms:
11.5 + x = 33.275366264

Solving
11.5 + x = 33.275366264

Solving for variable 'x'.

Move all terms containing x to the left, all other terms to the right.

Add '-11.5' to each side of the equation.
11.5 + -11.5 + x = 33.275366264 + -11.5

Combine like terms: 11.5 + -11.5 = 0.0
0.0 + x = 33.275366264 + -11.5
x = 33.275366264 + -11.5

Combine like terms: 33.275366264 + -11.5 = 21.775366264
x = 21.775366264

Simplifying
x = 21.775366264

Subproblem 2
x + 11.5 = -33.275366264

Simplifying
x + 11.5 = -33.275366264

Reorder the terms:
11.5 + x = -33.275366264

Solving
11.5 + x = -33.275366264

Solving for variable 'x'.

Move all terms containing x to the left, all other terms to the right.

Add '-11.5' to each side of the equation.
11.5 + -11.5 + x = -33.275366264 + -11.5

Combine like terms: 11.5 + -11.5 = 0.0
0.0 + x = -33.275366264 + -11.5
x = -33.275366264 + -11.5

Combine like terms: -33.275366264 + -11.5 = -44.775366264
x = -44.775366264

Simplifying
x = -44.775366264

Solution
The solution to the problem is based on the solutions
from the subproblems.
x = {21.775366264, -44.775366264}