(3k+3)(5k+35)=0

Solution for (3k+3)(5k+35)=0 equation:

(3k+3)(5k+35)=0

We multiply parentheses ..

(+15k^2+105k+15k+105)=0

We get rid of parentheses

15k^2+105k+15k+105=0

We add all the numbers together, and all the variables

15k^2+120k+105=0

a = 15; b = 120; c = +105;
Δ = b2-4ac
Δ = 1202-4·15·105
Δ = 8100
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$k_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$k_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{8100}=90$
$k_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(120)-90}{2*15}=\frac{-210}{30}
=-7
$
$k_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(120)+90}{2*15}=\frac{-30}{30}
=-1
$