The answer to your question would be that one hamburger costs $1.00 (h) and an order of fries would cost $0.75 (f)
You can check to make sure this is right by plugging your answers in the equations.
5(h)+3(f)=$7.25 ----> 5(1.00)+3(.75)=$7.25
3(h)+5(f)=$6.75 ----> 3(1.00)+5(.75)=$6.75
Hope this helps :)