The farmer took 8 days to cultivate one and a half hectares (15000 m^2)
so now divide 15000/8 which equals to 1875. so now we know that it takes him one day to cultivate 1875 m^2 which is 0.1875 hectares.
20 days = 0.1875 x 20
= 3.7500 hectares
hope it helped!