Answer: the cost per unit of gas is $0.38
Explanation:
Let x represent the cost per unit of electricity.
Let y represent the cost per unit of gas.
During one month, a homeowner used 600 units of electricity and 100 units of gas for a total cost of $344. It means that
600x + 100y = 344- - - - - - - - - -1
The next month, 400 units of electricity and 250 units of gas were used for a total cost of $299.
It means that
400x + 250y = 299- - - - - - - - - -1
Multiplying equation 1 by 400 and equation 2 by 600, it becomes
240000x + 40000y = 137600
240000x + 150000y = 179400
Subtracting, it becomes
- 110000y = - 41800
y = - 41800/- 110000
y = 0.38
Substituting y = 0.38 into equation 1, it becomes
600x + 100 × 0.38 = 344
600x + 38 = 344
600x = 344 - 38 = 306
x = 306/600
x = 0.51