Answer:
C. 1.29(16.5 + 4.5)
Explanation:
In order to find the total cost he spent you would have to combine the amount of mulch he bought and then multiply the total amount of mulch by the amount it costs per foot. The only equation that represents this is C. The 16.5 and 4.5 cubic feet are combined to see how many cubic feet of mulch he bought, and then the value is multiple by 1.29, the cost of mulch per cubic foot.
I hope this helps :)