please explain clearly I will give upvote

2. A new battery's voltage may be acceptable( A) or unacceptable (U). A certain flashlight requires two batteries, so batteries will be independently selected and tested until two acceptable ones have been found. Suppose that 90% of all batteries have acceptable voltages. Let Y denote the number of batteries tested. (a) What is f(2), that is P(Y = 2)? (b) What is f(3)?. Note that there are two different outcomes that result in Y = 3. (c) To have Y =5, what must be true of the fifth battery selected? List the four outcomes for which Y = 5 and then determine / (5). (d) Use the pattern in your answers for parts (a) (c) to obtain a general formula for /(y)