Pls answer ASAP.

You are remodeling your kitchen. you’ve contacted two tiling companies who gladly told you how long it took their workers to tile of a similar size jim completed half the floor in 8 hours. pete completed half of the other floor in 7 hours. if pete can lay 20 more tiles per hour than jim, at what rate can jim lay tiles

The sum of two numbers is 12 and their difference is 18 what are the two numbers

[10 points, algebra 2]according to my answer key the restrictions are -1 and 4. but why not positive 1?