A, B and C together can complete a certain work in 40 days.

Let total work = 1 unit.

A + B + C complete the work in 40 days.

Their one-day work = $1/40$

B + C complete the work in 72 days.

Their one-day work = $1/72$

So A's one-day work:

$1/40 - 1/72$

Taking LCM 360:

$=\frac{9-5}{360}$

$=\frac{4}{360}=\frac{1}{90}$

B is 50% more efficient than A.

So B's efficiency:

$B=\frac{3}{2}\times\frac{1}{90}$

$=\frac{1}{60}$

Now A, B and C work together for 16 days.

Work done in 16 days:

$16\times\frac{1}{40}=\frac{2}{5}$

Remaining work:

$1-\frac{2}{5}=\frac{3}{5}$

Time taken by B alone:

$\frac{3/5}{1/60}$

$=\frac{3}{5}\times 60$

=36