Slope is change in y over change in x. From 0 to 10 we change by 10 so 10/x=2. The change in x=5 but you’re not looking for the change in x. You’re looking for a value that would give you change in x being 5 which would be 0. 0 to 5 gives us a change in x of 5. 10/5 is 2 which is the slope.