Correct Answer - Option 3 : 9

**Given: **

Two men work equivalent to the work of five children.

Fifteen children take 9 days to finish work working for 2 hours a day.

**Formula used: **

1.) MDH/W is constant.

2.) M_{1} × D_{1} × H_{1}/W_{1} = M_{2} × D_{2} × H_{2}/W_{2}

Where,

M → The number of men

H → The number of hours

D → The number of days

W → The amount of work

**Calculation:**

2 men = 5 children

⇒ 4 men = 10 children

Work done by 15 children = 15 × 9 × 2 = 270

Work done by 4 men = work done by 10 children = 10 × 3 × d,

Where d is the number of days 4 men work for.

⇒ 270 = 30 d

⇒ d = 9

**∴ 4 men will work for 9 days.**