3x(x+10)+21=60

Solution for 3x(x+10)+21=60 equation:

3x(x+10)+21=60

We move all terms to the left:

3x(x+10)+21-(60)=0

We add all the numbers together, and all the variables

3x(x+10)-39=0

We multiply parentheses

3x^2+30x-39=0

a = 3; b = 30; c = -39;
Δ = b2-4ac
Δ = 302-4·3·(-39)
Δ = 1368
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{1368}=\sqrt{36*38}=\sqrt{36}*\sqrt{38}=6\sqrt{38}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(30)-6\sqrt{38}}{2*3}=\frac{-30-6\sqrt{38}}{6}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(30)+6\sqrt{38}}{2*3}=\frac{-30+6\sqrt{38}}{6}
$