there is still 1/5 of his crops that need to be harvested. to see how many days that will take divide that amount and see how many 1/10 fit into it. 1/10+ 1/10 = 2/10 which is also 1/5 so it will take 2 days.
if the base is 8 inches then your left with 120 and a triangle is seperated in 3 differnt parts so the 8 inches are already taken by the base so 120/2=60