If 8 men can reap 80 hectares in 24 days , then how many hectares can 36 men reap in 30 days?

Let the required no of hectares be x. Then 

More men, More hectares      (Direct proportion)

More days, More hectares      (Direct proportion)

  $Men8 : 36Days24:30⋮⋮ 80 :x$

=> ( 8 * 24 * x) = (36 * 30 * 80)

=>  x= 450