Solve for x: 5x - 3 = 2x + 12.

Collect the $x$ terms on one side: subtract $2x$ from both sides to get $3x-3=12$. Add $3$: $3x=15$. Divide by $3$: $x=5$, choice J. Check: $5(5)-3=22$ and $2(5)+12=22$. Choice G ($15$) stops at $3x=15$ and does not divide by $3$. Choice F ($3$) gives $12$ on the left and $18$ on the right, so it fails the check. Choice H ($9$) gives $42$ on the left and $30$ on the right, so it also fails. Always substitute your answer into both sides of the original equation.