Solve for one variable in either equation, then substitute it in the other equation to find the other variable.
-4x+9y=28 Add 4x to both sides 9y=28+4x Divide both sides by 9 y=(28+4x) / 9
-4x-y=-28 -4x- ((28+4x) / 9)= -28 -4x-28/9-4x/9=-28 Multiply everything by -9 to get rid of denominators (-9)(-4x)-(-9)(28/9)-(-9)(4x/9)=(-9)(-28) 36x+28+4x=252 40x+28=252 Subtract 28 from both sides 40x=224 Divide both sides by 40 x=5.6
Substitute x=5.6 back in to now solve for y. -4x+9y=28 (-4)(5.6)+9y=28 -22.4+9y=28 Add -22.4 to both sides 9y=50.4 Divide both sides by 9 y=5.6
To find the percent increase, you can divide the increase value by the original: 30/25 = 1.2 --> 120%. Next, since they ask for the percent of increase, you can subtract 1 or 100% from your answer which would give you a final answer of 20% increase.
Note that the graph is shaped like a V. The left half of the graph is decreasing from -∞ up until 0 when it hits the origin and starts to increase. Put this into interval notation: (-∞,0).
