The answer would be 16, because the delivery of the 8 trees costed 40, and the overall cost was 168, so you would subtract 40 for the delivery, and divide 128 by 8.
If the delivery was 168 in total the fee was also in there. 8x5=40 so thats the fee. Subtract that from 168 which is 128. So the cost of the trees total was 128 but the total cost of the fee is 168. Hope this helped.
