Question 551462
This problem is asking you to estimate. The amount of trees is not exact and the trees per row is not exact and we are asked for a reasonable number rather than an exact number

Let's guestimate. If he plants 10 trees for each row of 7 that'd be 70, close, but not enough, 11 would be 77, 12 would be 84 so 12 seems like a reasonable number.