Marvin counts six $5 bills. write each value that he counts. what pattern do you see in the one digits of the values he counts?

The first thing you should do is write down each value that Marvin has. We have then:
 5 + 5 + 5 + 5 + 5 + 5.
 We observe as pattern that the number is repeated six times. We can rewrite the operation as:
 5 * n
 Where,
 n = number of times the operation is repeated.
 
 5 + 5 + 5 + 5 + 5 + 5.
 5 * n

I’d say letter a..