Do you need to solve for "a number"?
Let's call it x. So (3/4)x + 1 = 5.
Subtract 1 from both sides because we want to separate that x from everything else.
(3/4)x = 4.
Multiply both sides by 4.
3x = 16.
Divide both sides by 3. x = 16/3.
To test it, (16/3)(3/4) + 1
(48/12) + 1
4 + 1
5