A does 80% of a work in 20 days. He then calls in B and they together finish the remaining work in 3 days. How long B alone would take to do the whole work?
A. \begin{aligned} 35\frac{1}{2} \end{aligned}
B. \begin{aligned} 36\frac{1}{2} \end{aligned}
C. \begin{aligned} 37\frac{1}{2} \end{aligned}
D. \begin{aligned} 38\frac{1}{2} \end{aligned}