Mathematics:

1 man's 1 day's work= $\frac{1}{16\times 24}=\frac{1}{384} part$

1 woman's I day's work= $\frac{1}{32\times 24} =\frac{1}{768}par$

Work done in 12 days by 16 and 16 women

$=12\left(\frac{16}{384}+\frac{16}{768}\right)=12\left(\frac{1}{24}+\frac{1}{48}\right)=\left(\frac{1}{2}+\frac{1}{4}\right)=\left(\frac{2+1}{4}\right)=\frac{3}{4}$ part 

Remaining work = $\left(1-\frac{3}{4}\right)=\left(\frac{4-3}{4}\right)=\frac{1}{4}$ part 

Again work done in 2 days by 16 men and 16 women 

$2\left(\frac{16}{384}\frac{16}{768}\right)=2\left(\frac{1}{24}+\frac{1}{48}\right)=\left(\frac{2+1}{24}\right)=\frac{3}{24}=\frac{1}{8}$ part 

Now remaining work= $\left(\frac{1}{4}-\frac{1}{8}\right)=\frac{1}{8}$ part 

Now, $\frac{1}{384}$ work is done in 1 day by = 1 man

$\frac{1}{8}work is done in 2 day by =\left(384\times \frac{1}{8}\times \frac{1}{2}\right)=24$ men . ans

Let, the speed of the train during returning journey be x kmph 

Speed during onward journey=  $(x+ 25\% of x)=\left(x+ \frac{25x}{100}\right)=\frac{5x}{4}$ kmph 

Distance covered in onward journey = $\frac{800}{2}=400 km$

Time taken by the train on onward journey= $\frac{{\displaystyle \frac{400}{5x}}}{4}$ hours [As, time= Distance/Speed]

And time by the train in returning journey = $\frac{400}{x}$ hours

According to the question,

$$\begin{gathered} \frac{{\displaystyle \frac{400}{5x}}}{4}+\frac{400}{x} =16 \\ \Rightarrow \left(\frac{400}{1}\times \frac{4}{5x}\right)+\frac{400}{x}=16 \\ \Rightarrow \frac{320}{x}+\frac{400}{x}=16 \\ \Rightarrow \frac{320+400}{x}=16 \\ \Rightarrow 16x=720 \\ \therefore x=45 kmph \end{gathered}$$

Speed of the train in the onward journey=$\frac{5x}{4}=\frac{5\times 45}{4}=56.25$ kmph