4/5 x 2= 8/5
Which is 1 3/5 cups needed for 2 pies
So (positive integer)-x-y can be negative
so to get a negative number as your result/answer, x+y must be greater than (positve integer) so for example
lets say (positive integer)=8
x+y must be greater than 8 to make the equation negative so
example
x=5
y=4
x+y=9
8-9=-1