2/5 are children

Remainder = 1 - 2/5 = 3/5

1/6 of remainder are men
1/6 x 3/5 = 3/30 = 1/10

So 1/10 of total number of people are men.

Difference between children and men
= 2/5 - 1/10
= 3/10

3/10 of total = 42
1/10 = 42 ÷ 3 = 14
Total = 14 x 10 = 140

Or

Total = 42 x 10/3 = 140

Another method :

There are two fractions in the question, one with denominator 5, the other 6.

We find the common multiple of 5 and 6

5 x 6 = 30

children = 2/5 = 12/30

Let total be 30u. So children = 12u.

Remainder = 30u - 12u = 18u

Men = 1/6 of remainder
= 18u ÷ 6
= 3u

Difference between men and children
= 12u - 3u
= 9u

9u = 42
3u = 42 ÷ 3 = 14

So total = 30u
= 3u x 10
= 14 x 10
= 140