What is the answer to -g + 2 (3 + g ) = -4 (g+ 1 )

Which undefined geometric term is described as a location on a coordinate plane that is designed by an ordered pair (x, y) ?

Two planes leave an airport at the same time, one flying east, the other flying west. the eastbound plane travels 20 mph slower. they are 1600 mi apart after 2 hr. find the speed of each plane.

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