Question

Keisha had two pieces of ribbon of equal length. She cut
the first piece of ribbon into 15 equal parts. She also cut the second
piece of ribbon into equal parts. Nine parts of the first piece are
equal in length to 3 parts of the second piece. Into how many parts
did she cut the second piece of ribbon?

Answer 1

"Nine parts of the first piece are
equal in length to 3 parts of the second piece. "
means that each part of the second ribbon is three times as long as each part of the first, which also means that the number of parts of the second ribbon is one-third of the number of parts of the first.
I'll let you take it from here.

Answer 2

1/3*15=5