how to solve this word problem

Question

A university bookstore recently sold a wirebound graph-paper notebook for $1.10, and a college ruled notebook for $3.16. At the start of spring semester a combonation of 50 of these notebooks were sold for a total of $102.38. How many of each type were sold?

Answer 1

1.1nb + 3.16rb = 102.38

nb + rb = 50 ⇒ nb = 50 - rb                               nb- notebook

1.1( 50 - rb) + 3.16rb = 102.38                          rb- ruled notebook

55 - 1.1rb + 3.16rb = 102.38

2.06rb = 102.38 - 55 = 47.38

rb = 47.38/2.06

rb = 23

nb = 50 - rb = 50 - 23

nb = 27