How to find tables that can seat six people

Question

There are 15 tables in Brown House Cafe. Some of these tables can seat six people, and the rest can only sit four people. If a maximum of 76 people can be seated in Brown House Cafe, how many six-people tables does the cafe have?

Answer 1

Let S = # of 6 seat tables & F = # of 4's

S + F = 15

6S + 4F = 76

Multiply the first equation by 4 and subtract it from the second equation

4S + 4F = 60

2S = 16

S = 8

F = 7