Answer: x = 18
=====================================
Work Shown:
3/4 = x/24
3*24 = 4x ... cross multiply
72 = 4x
4x = 72
x = 72/4 ... divide both sides by 4
x = 18
---------
As a check,
3/4 = 0.75
x/24 = 18/24 = 0.75
Both result in the same decimal value, so 3/4 = 18/24 is a true equation.