Answer:the amount of money that he spent on parts for his lawnmower is $33
Explanation:
Let x represent the amount of money that he spent on parts for his lawnmower.
On Monday he spent $56 for gas for his lawnmower.
The total revenue that he got from Monday to Friday would be the sum of the amount made from the two lawns that he cut on Tuesday, the three lawns that he cut on Wednesday and the one lawn that he cut on Friday. Therefore,
Revenue = 40 + 60 + 20 = $120
The total cost from Monday to Friday would be the sum of the amount spent on buying gas on Monday and the amount spent on parts to fix the lawnmower on Thursday. Therefore,
Total cost = 56 + x
Profit = revenue - cost
If the overall value in his account for the week was $31, therefore,
120 - (56 + x) = 31
120 - 56 - x = 31
- x = 31 + 56 - 120 = -33
x = $33