Answer: 25 bikes and 55 cars were used.
Step-by-step explanation:
Let b represent number of bicycles that the students ride to school.
Let c represent number of cars that the students drive to school.
At Billy's school, 80 students come to school by bike or car. It means that
b + c = 80
A bike has 2 wheels. A car has 4 wheels. Together the vehicles that arrive at the school have 270 wheels. It means that
2b + 4c = 270- - - - - - - - - - 1
Substituting b = 80 - c into equation 1, it becomes
2(80 - c) + 4c = 270
160 - 2c + 4c = 270
- 2c + 4c = 270 - 160
2c = 110
c = 110/2
c = 55
b = 80 - c = 80 - 55
b = 25
