algebra i dont understand

Question

If g(x) = 3x-1 and if g(a) = 7, then which of the following is the value of a

Answer 1

g(x) = 3x - 1 and g(a) = 7

Plug in "a" for "x". Then you get g(a) = 3a - 1. Set 3a - 1 and 7 equal to each other.

3a - 1 = 7 → 3a = 8 → a = 8/3