Tim: $475
Wayne: $325

One idea to do for part b is unit-part (but note: this is already pitting itself against Secondary level approaches in level of difficulty)

Amount of money spent by Tim: 3 units
Amount of money spend by Wayne: 5 units

Amount of money Tim had left: 2 parts
Amount of money Wayne had left: 1 part

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3 units + 2 parts = 475 (do you know why?)
5 units + 1 part = 325 (do you know why?)

We now make the "parts" in both of the above equal (we make them "2 parts".

5 units + 1 part = 325 means that...
10 units + 2 parts = 650 (do you know why?)

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Ok, so now we have the following.

10 units + 2 parts = 650
3 units + 2 parts = 475

The difference between the two scenarios is 7 units with a value of 175.

7 units --> 175
1 unit --> 25
3 units --> 75 (amount Tim spent)

So it's clear that Tim spent $75 out of his $475, a fraction equal to 75/475 or 3/19.