'A' can do a piece of work in 15 days, which 'B' can do in 10 days. 'B' worked at it for 8 days. 'A' can finish the remaining work in

3 days

Total work = LCM of 15, 10 = 30

Efficiency of A = 30/15 = 2

Efficiency of B = 30/10 = 3

B work in 8 days

⇒ 8 × 3

⇒ 24

Remaining work = 30 – 24 = 6

A  will complete the remaining work =  6/2 = 3 days