From the question we are given the cost of five batteries and 7 batteries
The total cost of five batteries is $4.50
The total cost of seven batteries is $6.30
Each battery will cost = total cost of the batteries / the total number of the batteries
For 7 batteries
The total cost of 7 batteries $6.30
Total number of batteries = 7
The cost for each battery = 6.30/7
The cost for each battery is $0.9
One battery will cost $0.9
The total cost for x batteries
Let y represent the total cost
x represent the number of batteries
Y = 0.9* x
Y = 0.9x
The linear equation is y = 0.9x