There should be sixteen branches. There are four possible suits for the first card, hearts, diamonds, clubs, spades. Then each of those four branches has four branches for the second card drawn. 4*4 = 16.
Let s represent the number of sales, and t the total pay
the equation to represent this situation is t = 2s + 50
so set t to 100, and solve for s
100 = 2s + 50
50 = 2s
25 = s
you need to make at least 25 sales