Your equation is:
f(x) = 7x - 2
Solve for x.
Add 2 to both sides of this equation to get:
f(x) + 2 = 7x
Divide both sides of this equation by 7 to get:
(f(x) + 2)/7 = x
Since, in general, a = b implies that b = a, this equation becomes:
x = (f(x) + 2)/7
Replace x with f(x) and replace f(x) with x to get:
f(x) = (x+2)/7
That's your inverse function.
Graph both your function and your inverse function.
Set y = f(x) to get:
y = 7x - 2 (your regular function).
y = (x+2)/7 (your inverse function).
Graph also the function y = x.