6. (Bonus question) A grocery store is running a sales promotion Where a customer will receive one of the letters A, E, L, S, U and V for each purchase. The letters are given away randomly by cashier. If a customer collects all six letters (\"VALUES\"), he / she will get a coupon of $10 that can be used in the store. What is the expected number of purchases need to get a coupon. (Hint: Let X be the number of purchases need to collect all six letters. Let X:- be the number of purchases to get the ith letter, for 7::13w36 So,X:X1+X2l+X5 )