t = the number of hours
7t - 3 ≥ 39
[He charges $7 per hour(t), he spends $3 in equipment fees, and he wants to earn at least $39(this is the minimum, so he can earn more than $39).]
Now you need to solve for t (isolate/get t by itself):
7t - 3 ≥ 39 Add 3 on both sides
7t - 3 + 3 ≥ 39 + 3
7t ≥ 42 Divide 7 on both sides
t ≥ 6
(the question says "what are the possible numbers of hours Jose could trim trees" so I'm not sure if they are looking for more answers, sorry)
