This is a simultaneous question.
To solve this, we have to make up 2 equations based on the info provided like so:
electricity = e
gas = g
600e + 100g = $412 ——(1)
400e + 150g = $293 ——(2)
In this case, it’ll be easier to use the elimination method where you eliminate a variable so you can calculate only one.
Here, we will be eliminating e so we can get the cost of gas.
To do this we need to get both equation’s e to 600, so we have to multiply equation 2 by 1.5:
(2) x 1.5:
400e + 150g = $293
600e + 225g = $439.50 ——(3)
Now we eliminate e by subtracting equation 1 from equation 3:
(3) - (1):
600e + 225g - 600e - 100g = $439.50 -$412
125g = $27.50
g = $0.22.
Therefore one unit of gas costs $0.22.
Hope it helps and have a good day ahead :D
