If x and y are both positive, when is x-y negative? if x and y are both negative, when is x-y positive?

Use the elimination method to solve the systems of equations.choose the correct ordered pair. 7x+4y=39

At store a, erasers are sold individually. the cost y of x erasers is represented by the equation y=0.75x. the costs of erasers at store b are shown in the graph.

Which is greater or equal 312 mg or 312 dg