A can do 20% of work in 4 days, B can do 331/3\% of the same work in 10 days. They worked together for 9 days. C completed the remaining work in 6 days. B and C together complete 75% of the same work in:

Answer: Option C

A = 20 days
B = 30 days

(A + B) × 9 + C × 6 = 60
(3 + 2) × 9 + C × 6 = 60
C = $$\frac{5}{2}$$ unit
C = $$\frac{60\times 2}{5}$$  = 24 days
(B + C) × x = 60 × $$\frac{3}{4}$$
$$\left(2+\frac{5}{2}\right)\text{x}=45$$
9x = 90
x = 10 days