Explanation:

15 men --------- 10 days

1 man --------- 150 days

10 men --------- 15 days

20 boys --------- 15 days

1 boy --------- 300 days

10 boys --------- 30 days
now 10 men takes 15 days

so in one day they complete 1/15 of work 

10 boys takes 30 days

so in one day they complete 1/30 of work 

both together completes the work in one day = 1/15 + 1/30

= 45 / 15 ×30 = 1/10 of work 

so together they fulfil the work in 10 days

Hence, option 2 is the correct answer.