Answer:
a) 
b) 
c) Yes.
Step-by-step explanation:
We have that:

And we have $10 free of taxes.
Making x= number of tires to buy, then we have that the total cost of tires is:

So, what we pay for taxes is given by:

a) Then, according to the above, we can write down the total cost before the discount as:

b) And the total cost after discounts, is then given by:

c) If the discount is added first, then less tax will be paid because the amount on which it is paid is lower. If the discount is added later, then the taxes will have been taxed on a higher amount, so it does matter whether they are added first or later.
1999+1001=3000 1091+1009=3000 2000+1000=3000
3000-1001=1999 3000-1009=1091 3000-2000=1000
To make a fraction into simplest form you have to find the greatest common factor. In this case it is 5. So then you divide both the numerator and the denominator by the greatest common factor of 5.
15÷5=3
100÷5=20
There is no factors that go into both 3 and 20 so simplest form is 3/20.
35 is the number you can remove so you can still have the same median