To solve this, you need to isolate/get the variable "a" by itself in the equation:
3(a - 5) = 18 Divide 3 on both sides
[tex]\frac{3(a-5)}{3} =\frac{18}{3}[/tex]
a - 5 = 6 Add 5 on both sides to get "a" by itself
a - 5 + 5 = 6 + 5
a = 11
PROOF
3(a - 5) = 18 Substitute/plug in 11 into "a" since z = 11
3(11 - 5) = 18
3(6) = 18
18 = 18
