Probability Question.

Four technicians regularly make repairs when breakdowns occur on an automated production line. Amy, who services 20% of the breakdowns, make incomplete repair 1 time in 20; Bradley, who services 50% of the breakdowns, make incomplete repair 1 time in 10; Cathy, who services 25% of the breakdowns, make incomplete repair 1 time in 10; Don, who services 5% of the breakdowns, make incomplete repair 1 time in 20. For the next problem with the production line diagnosed as being due to an initial repair that was incomplete, what is the probability that this initial repair was made by Cathy?

This is only from a first/second year class "Intro to Applied Statistics", and we just started probability.