You need to find the common denominator.
5/7 = 40/56
6/8 = 42/56
http://www.mathsisfun.com/numbers/common-denominator.html
show how 30/56 is smaller than 5/7 and 6/8
2 answers
5/7=(8*5)/(8*7)=40/56
6/8=(7*6)/(7*8)=42/56
30/56 < 40/56
30/56 < 42/56
6/8=(7*6)/(7*8)=42/56
30/56 < 40/56
30/56 < 42/56