Ok first let's write everything down we can into equations. Let each stand for the price that each boy paid. From the first sentence, . Now for the rest.

"The first boy paid one half of the sum of the amounts paid by the other boys."

. See how that worked?

For the second boy, it's very similar just one-third of the total of the others.

And for the third,

So, now we have 4 variables and 4 equations and we can solve for each of them.

You with me so far?