4/4 would equal 160.
Use proportions to solve this answer, like John McCann did above.
(3/4)/120 = (4/4)/x
We use x because 4/4 isn't given a number, while 3/4 is.
(3/4)/120 = 1/x
3/4 = 120 * (1/x)
3/4 = 120/x
(3/4) * x = (120/x) * x
3x/4 = 120
(3x/4) * 4 = 120 * 4
3x = 480
3x/3 = 480/3
x = 160 <--- 4/4 would equal to 160 is 3/4 was equal to 120.