Explanation:
v(x) = y = -3/4x - 1/3
y + 1/3 = -3/4x
x = -4/3 × (y + 1/3)
you see ? we only need to show how we calculate x out of y (instead of the normal direction of y or of x).
and to follow naming standards we now simply switch x and y, so that the inverse function is indeed again a function of x
y = -4/3 × (x + 1/3) = -4x/3 - 4/9