A can do three times of the work done by B in one day. They together finish \(\frac{2}{5}\)th part of the work in 9 days. The number of days in which B can do the work alone is:

90

                   A   :   B   :   (A + B)

Efficiency:   3   :   1   :       4

ATQ,

(A + B) can do \(\frac{2}{5}\) of the work in ⇒ 9 days

(A + B) can do 01 work in ⇒ 9 × \(\frac{5}{2}\) = \(\frac{45}{2}\) days

Now, Total Work = Time × Efficiency = \(\frac{45}{2}\) × 4 = 90

B alone can do it in ⇒ \(\frac{90}{1}\) = 90 days