Correct Answer - Option 2 : 6

**Given:**

X and Y can finish a work in 15 days and 30 days respectively. Both of them worked for 5 days and left. The remaining work was completed by Z in 5 days.

**Formula:**

If A and B can together finish it in t days with A and B finishing the work in a and b days respectively,

1/a + 1/b = 1/t

**Calculation:**

Let total work be 30 units, LCM of 15 and 30.

Efficiency X = 30/15 = 2

Efficiency Y = 30/30 = 1

Let the efficiency of Z be z

ATQ,

⇒ 5(2 + 1) + 5z = 30

⇒ 15 + 5z = 30

⇒ 5z = 15

⇒ z = 3

∴ Required time = 30/3 + 2 = 30/5 = 6 days.