Answer
$x=-1,3$
See graph.
Work Step by Step
Step 1. Given $f(x)=x^2+3x$ and $g(x)=5x+3$, let $f(x)=g(x)$ to get $x^2+3x=5x+3$ or $x^2-2x-3=0$
Step 2. Factor and solve the equation $(x-3)(x+1)=0$, thus $x=-1,3$ and $y=-2,18$ or $(-1,-2),(3,18)$
Step 3. See graph.
