Karina uses the system of equations below to compare the monthly utility costs in July and December for electricity, x, and natural gas, y. 750x + 17y = 141.61
300x + 30y = 75.90
Karina solves the system using linear combination and arrives at the equation 116y = 96.28. She then solves this equation for y. Which statement explains Karina’s solution?

The cost of natural gas is $0.17 per unit.
The cost of natural gas is $0.20 per unit.
The cost of natural gas is $0.72 per unit.
The cost of natural gas is $0.83 per unit.