During one month, a homeowner used 200 units of electricity and 140 units of gas for a total cost of $74.40. The next month, 280 units of electricity and 150 units of gas were used for a total cost of $96.80. Find the cost per unit of gas.

cost per unit of electricity = x

cost per unit of gas = y

200x + 140y = 74.4

280x + 150y = 96.8

eq. 1 * 7 - eq. 2 *5

980y - 750y = 520.8 - 484

=> 230 y = 36.8

=> y = 0.16

cost of one unit of gas = $0.16