The task is to generate the correct answer for a given math problem.

Problem: a man is 28 years older than his son . in two years , his age will be twice the age of his son . the present age of the son is ?
26

Problem: what is the units digit of 17 ^ 83 × 13 ^ 82 × 11 ^ 67 ?
4

Problem: 9 men working 8 hours per day dig 30 m deep . how many extra men should be put to dig to a depth of 50 m working 6 hours per day ?

11