-(3-a)(2+5)=-1

Solution for -(3-a)(2+5)=-1 equation:

Simplifying
-1(3 + -1a)(2 + 5) = -1

Combine like terms: 2 + 5 = 7
-1(3 + -1a)(7) = -1

Reorder the terms for easier multiplication:
-1 * 7(3 + -1a) = -1

Multiply -1 * 7
-7(3 + -1a) = -1
(3 * -7 + -1a * -7) = -1
(-21 + 7a) = -1

Solving
-21 + 7a = -1

Solving for variable 'a'.

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

Add '21' to each side of the equation.
-21 + 21 + 7a = -1 + 21

Combine like terms: -21 + 21 = 0
0 + 7a = -1 + 21
7a = -1 + 21

Combine like terms: -1 + 21 = 20
7a = 20

Divide each side by '7'.
a = 2.857142857

Simplifying
a = 2.857142857