You have the following function:
g(x) = 3x - 7
In order to determine th value of x when g(x) = -4, you equal the previous expression to -4 and solve for x, just as follow:
g(x) = 3x - 7 replace g(x) = -4
-4 = 3x - 7 add 7 both sides
-4 + 7 = 3x simplify
3 = 3x divide by 3 both sides
3/3 = x
x = 1
Hence, the anser is x = 1