45 men working 9 hours per day dig 40 m deep. How many extra men should be put to dig to a depth of 56 m working 7 hours per day ?

45 men working 9 hours per day dig 40 m deep. How many extra men should be put to dig to a depth of 56 m working 7 hours per day ? Correct Answer 36

(45 x 9)/40 = (M x 7)/56 => M = 81

=> 81 – 45 = 36