28. If the ratio of a to b is 4 to 5 and the ratio of a to c is 6 to 11, what is the ratio of b to c?

You have

a/b = 4/5
a/c = 6/11

You want b/c
= (b/a)/(c/a)
= b/a * a/c
= 5/4 * 6/11
= 30/44 = 15/22