Let, S = Shirt, J = Jeans
14a)
This question asks for the discount to be added after everything else.
S= 12 J=19
3S + 2J -3 = Cost with discount applied to total
^ This expression adds to costs, then takes away the $3 discount as the end.
14b)
This questions says the discount is added on every shirt, we get a similar expression:
3(S-3) + 2(J-3) = Cost with discount applied on every shirt and jeans
14c)
The difference between a) and b) is that:
> the discount in a) is applied on the total, meaning a lower discount
> the discount for b) is applied on each shirt and jeans, meaning a greater discount
14d)
If I were the shop owner I would be more specific of what the discount included, for example we don't know whether to discount each product (shirts and jeans) or only discount the total.