If 4 men reap 40 acres in 30 days, how many acres will 18 men reap in 12 days ?

By Direct approach :
More men, more acres
More days, more acres
so,
4 / 18 : 30 / 12 = 40 / x
x = (18 x 12 x 40) / (4 x 30)
72 acres