At a bargain store, tanya bought 3 items that each cost the same amount. tony bought 4 items that each cost the same amount, but each was $2.25 less than the items that tanya bought. both tanya and tony paid the same amount of money. what was the individual cost of each person's items?

To start out the equation you know that they both spent the same. The right of the equal sign is what Tanya spent and to the left was what Tony spent.
3x = 4(x-2.25)

If you solve it you get x = $9
Now that is what the cost was for each item that Tanya bought. The number in parenthesis() is what Tony spent on each item. 
Plug in 9 to x in (x-2.25)
You should get $6.75 for the amount of each item Tony spent.

Dwould be the answer