The equation given in the question is
y = 5 - 3x
To find the inverse, we have to replace x with y.
x = 5 - 3y
-3y = x - 5
Dividing both sides by - 3 we get
y = (x - 5)/-3
I hope that the procedure is clear enough for you to understand and this is the answer that you were looking for and the answer has actually come to your desired help.