A can complete a certain piece of work in 40 days. B is 25% more efficient than A and C is 28% more efficient than B. They work together for 5 days. The remaining work will be completed by B alone, in:

Let the efficiency of A be x.

Efficiency of B = 25% more efficient than A = 1.25x

Efficiency of C = 28% more efficient than B = $$1.25x \times \frac{128}{100}$$ = 1.6x

Efficiency ratio of A, B and C = x: 1.25x : 1.6x = 20 : 25  :32

Total work = efficiency $$\times$$ time = 20 $$\times$$ 40 = 800 units 

5 days work = (20 + 25 + 32) $$\times 5 = 77\times$$ 5 = 385 units

Remaining work = 800 - 385 = 415 units

Time taken to complete work by B = 415/25 = $$16\frac{3}{5}$$