One of the joys of maths is that there are a whole lot of different ways of writing down the same number. It can also be a pain, sometimes.
3/4 can be written in literally an infinite number of ways. To find an equivalent fraction, you just multiply the numerator (the number on top) and the denominator (the number on the bottom) by the same amount. This works as fractions multiply as follows:
(a/b) x (c/d) = (ac)/(bd)
So if you have your fraction of 3/4 and you multiply it by say 2/2 (which equals 1, so doesn't change the value of the fraction) then you get (3x2) / (4x2) = 6/8.
One interesting aspect of this is that if you multiply top and bottom by 25 then you get:
which is the same as 0.75 in decimal, which is the same as 3/4