I recommend you solve this three different ways, if possible.

By formula.

By tree diagram (this is the easy way).

By Venn diagram.

There are benefits to doing this problem several different ways - but - I admit, though, that this is a Herculean task for some [including me] so there is some risk of brain damage. . .

Deciding to take on this challenge is a cost/risk/benefit tradeoff, as are many decisions. But if you succeed your understanding of what "The Rev" preached will be rock-solid.