A contract is to be completed in 56 days and 104 men are set to work. Each working 8 hours a day, after 30 days, 2/5th of the work is finished. How many additional men may be employed so that work may be completed on time, each man now working 9 hours per day?

Let 'W' be the amount of work. It is given that,

$$\dfrac{2}{5}*W = 104*8*30$$ ... (1)

Let 'X' be the number of additional men required to finish the work on time. 

$$W - \dfrac{2}{5}*W = (104+x)*9*(56-30)$$ ... (2)

By equation (1) and (2) we can say that, 

$$\dfrac{2}{3} = \dfrac{104*8*30}{(104+x)*9*(56-30)}$$

$$\Rightarrow$$ $$(104+x)*9*26 = 12*104*30$$

$$\Rightarrow$$ $$(104+x)=160$$

$$\Rightarrow$$ $$x=56$$.

Hence, option A is the correct answer.