find the following probability

A train of **n **wagons transports hazardous materials. Each wagon, and independently

from the others, has a probability **p** to be defective. Prior to the train’s departure all

wagons are examined by two inspectors who do not exchange their inspection’s results during the control. We assume that each inspector will detect a default on a given wagon (if any) with probability** r**. One default is enough to delay the train’s departure(for repair). Compute the following probabilities.

that the train’s departure will be delayed?

do I use the conditional prob formula here, P(A|B) where B is the prob that the inspector will find a default, and A is the train will be delayed?

but how do I find the prob of A and B?