Five hamburgers and three orders of french fries cost $7.25, and five orders of french fries and three hamburgers cost $6.75. how much will it cost to buy one hamburger and one order of french fries?

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 :)