We are asked to get the maximum number of things within a fixed amount of money. To get the maximum number of products, we have to maximize the number of products of lowest price.
cheaper price is 2$ and we have to buy the products exactly with 25$.
25/2=12.5 , If we buy 12 pair brand X socks, 12*2=24, we have 1$ left. But that cant be happened!!
If we buy 11 pair brand X socks 11*2=22, we have left 3$ buy which we can buy a pair of brand y socks. So total 11+1 =12 pair
similar to the 1st one:
65/3=21+something...., so 21*3=63, 2$ left; so it is not acceptable!!
next,20*3=60, 5$ left, we can not buy Product B with 5 $ ;so it is not acceptable
19*3=57$, 8$ left by which we can buy 2 package of B, so total 19+2=21(E)