Answer
$x=1 \text{ or } x=-3$
Work Step by Step
Subtract $4x$ and add $4$ to both sides f the equation to have:
$5x^2+10x-15=15-15
\\5x^2+10x-15=0
\\5(x^2+2x-3)=0$
Divide 5 to both sides of the equation to have:
x^2+2x-3=04
Factor the trinomial to have:
$(x-1)(x+3)=0$
Equate each unique factor to zero then solve each equation to have:
$x-1=0 \text{ or } x+3=0
\\x=1 \text{ or } x = -3$
