To find equal fractions, multiply the numerator and denominator by the same number. In this case, you should multiply by 4/3:
45 x 4/3 = 60
48 x 4/3 = 64
= 60/64
It does not matter what number you choose to multiply by, as long as you do it to both the numerator and denominator. In a situation like this, to figure out which number to multiply by when you already have an answer, simply divide either the numerator or denominator by the corresponding numerator or denominator in the answer. Example:
60/45 = 4/3
Hope this helps!
~ArchimedesEleven