Let x be the price of Tanya's item. Tanya spent 5x, because she bought 5 of them.
The cost of Tony's item is x-1.75, because the price is 1.75 less than Tanya's. He spent 6(x-1.75), because he bought 6 of them.
They spent the same amount of money, so we have
[tex]5x=6(x-1.75) \iff 5x=6x-10.5 \iff -x=-10.5\iff x=10.5[/tex]
So, Tanya's item costs 10.5, and Tony's item costs 8.75.
In fact, we have
[tex]10.5\cdot 5 = 52.5 = 8.75\cdot 6[/tex]