If wheat requires 7.5 cm of water after every 28 days

If wheat requires 7.5 cm of water after every 28 days and the base period for wheat is 140 days, what is the value of delta for wheat?

[A] 7.5 cm
[B] 27.5 cm
[C] 37.5 cm
[D] 17.5 cm

ANSWER= [C] 37.5 cm

Delta for Wheat = (140/28) × 7.5

Delta for Wheat = 37.5 cm