If it takes 40 laborers to to harvest a land of area 9600 m2 in 12 hours time then, assuming they all work at the same rate (or getting an average rate) each completes at 9600/40= 240 square meters in 12 hours and so 240/12= 20 square m per hour. To do 17600 m at that rate would take one worker 17600/20= 880 hours. To do it in 10 hours would require 880/10= 88 workers, exactly what you got.
Cake for hiking? Wouldn't protein be better?2.
If 48 Kg of cake can fill up 9 boys for a mountain hike of 4 hours, then how many hours of hiking can 120Kg of cake fill up 15 boys?
9 boys consume 48 Kg / 4 hours
Then 15 boys will consume how much 120Kg/ X hours
Number of hours = 9 x 120 x 4 / 48 x 15 = 6 hours.
Any feedback on this method?
Again, it would be better to say what each step is rather than just writing one long computation.
48 kg of cake amoung 9 boys is 48/9= 16/3 kg per boy. Lasting 4 hours, that is (16/3)/4= 4/3 kg per boy per hour. Now go back the other way. 120 kg divided by 4/3 kg/(boy hour), in order to cancel "kg" is 90 boy-hours. Divided among 15 boys that is 90/15= 6 hours. The 120 kg will last 5 boys 6 hours.
Both of your answers is correct so you "method" is correct. I would only say that your "method" is not stated very clearly. Especially if you are turning this in as homework, it would be better to explain each step.