a:b = 8:5 b:c = 3:4
since both sides have b. make b the same. multiply the left by the right side b value of 3 and multiply the right by the left side b value of 5.
3(a:b) and 5(b:c)
3 (8:5) and 5(3:4)
24:15 15:20
now that both sides have the same b value
a:b:c = 24:15:20
