Seven is the number of eights you are seeking.
5 3/8
5/8 of 72 is 45.
six
7 eights or 56
40/8 = 5
11 sixteenths
There are 40 eights in 5.
2 eights and 5 eights
5/8*x=100 x=800/5 x=160
3/8 will never equal 5/8. But if you mean what number can you multiply 3/8 by to get 5/8, that number is about 1.666666666... (1 with infinite 6's after the decimal), or simply, 1 and 2/3.
Three eights of a number (x) is x 3/8.