Let the number of movie receipts be x and number of popcorn receipts be y.
It is also given that he spent 220.50 altogether.
Let the price of popcorn be z.
It is also given that on three occasions, he did not buy popcorn so it follows:
Add (i) and (iii) to get:
So it follows:
Substitute the values x=24 and y=21 in (ii) to get:
So each bag of popcorn costed approximately 1.55 dollars.