Parallel first order reaction
Ok, there are two reactions for the 2 moles of A

$$\ce{A -&gt;[rate\space =\space k_1] 2B}$$

$$\ce{A -&gt;[rate\space =\space k_2] 2C}$$

$$\dfrac{k_1}{k_2} = \dfrac{1}{2}$$

The question asks for the total number of moles of A+B+C when the reaction is 75% complete.


At that point 25% of A remains or 0.5 moles of A
It does matter what the ratio of B and C produced is since either reaction of A creates 2 moles of product.  So there is 2*1.5 = 3 moles of product (B+C).


Thus there is 0.5 + 3 = 3.5 moles of A+B+C in the solution when the reaction is 75% complete. 

There are 4 moles when the reaction is 100% complete. 

So the book answer is wrong.