I think the important idea to stress is that it's more than, not just more. So, in this case, it's more than dimes. The fact that quarters is in there in the middle is just to explain what he has that numbers 8 more than dimes.

One trick I use to explain things is to drop out unnecessary parts and figure it out, then add things back in to see how they should affect the sentence. (e.g., if someone says "Charlie told Frank and I", if you drop Frank out, you'd get "Charlie told I" which is more clearly wrong. Adding Frank back in doesn't change me to I.)

So, if they drop the quarters (for the moment), they can put more and then together to see what needs to be added -- 8 and dimes. Then, when they ask what that equals, you add back in the quarters -- The quarters number 8 more than dimes.

I think the important idea to stress is that it's more than, not just more. So, in this case, it's more than dimes. The fact that quarters is in there in the middle is just to explain what he has that numbers 8 more than dimes.

One trick I use to explain things is to drop out unnecessary parts and figure it out, then add things back in to see how they should affect the sentence. (e.g., if someone says "Charlie told Frank and I", if you drop Frank out, you'd get "Charlie told I" which is more clearly wrong. Adding Frank back in doesn't change me to I.)

So, if they drop the quarters (for the moment), they can put more and than together to see what needs to be added -- 8 and dimes. Then, when they ask what that equals, you add back in the quarters -- The quarters number 8 more than dimes.