What is the equation in slope intercept form

What's the difference between: x≥0 and nonnegative integer. ?

An unknown number of kids and buses are getting assigned. when assigning 4 kids to each bus, there are 2 kids that aren't placed in a bus. when assigning 8 kids to each bus, there are 2 empty buses. how many total kids are there?

What is the solution to the system of equations? (–2, –8) (–1, –5) (0, –2) (2, 4)