B. multiply the whole thing for the area then divide by two bcs its a triangle
5(a-1) - 15 = 3(a+2) + 4
Open all parenthesis and distribute
5a - 5 - 15 = 3a + 6 + 4
Simplify
5a - 20 = 3a + 10
Add both sides by 20 and subtract both sides by 3a
2a = 30
a = 15