assuming one transaction usually involves a food and a drink. Everything from drinks to food to chips to sweets is increased by .50.
A lot of applied math is just writing down potentially relevant information in an orderly way.
[MATH]\text {# of transactions per day} = 250.[/MATH]
[MATH]\text {average # of items currently sold per transaction} = 2.[/MATH]
[MATH]\text {aggregate sales per day in dollars at current prices} = 5000.00.[/MATH]
Now you can start to calculate:
[MATH]\text {# of items currently sold per day} = 2 \times 250 = 500.[/MATH]
[MATH]\text {average current price per item in dollars} = \dfrac{5000.00}{500} = 10.00.[/MATH]
[MATH]\text {average price per item in dollars after increase of 50 cents} =[/MATH]
[MATH]10.00 + 0.50 = 10.50.[/MATH]
[MATH]\text {Aggregate sales per day in dollars at increased prices assuming no reduction in demand} =[/MATH]
[MATH]10.50 \times 500 = 5250.00.[/MATH]
[MATH]\text {Reduction in items sold that will offset price increase} = 500 - \dfrac{5000}{10.50} = 24 \text { approximately}.[/MATH]
That final calculation may not give you an exact answer, but it will be a close approximation.
[MATH]10.50 \times (500 - 24) = 10.50 \times 476 = 4998.00[/MATH]