What is the equation of the following line?

How do i work this problem out using the equation a=pe^rt

Astandard deck of cards contains 52 cards. one card is selected from the deck. (a) compute the probability of randomly selecting a seven or king. (b) compute the probability of randomly selecting a seven or king or jack. (c) compute the probability of randomly selecting a queen or spade.

What is the length of the unknown leg in the right triangle ?