This is an example of Additionproperty between two positive integers (i.e. whole value numbers), which means the result will be positive and larger than the two numbers.
The result of the addition would be:
Another way to do it if you are struggling a bit you can write the value of as so then you can say:
I think she is gonna have to pay $14 because if you divide the number it costs by the number of pounds she bought, you get the price per pound. Not sure though.