x + y = 7
2x - 3y = -21

Answer:
one solution
Step-by-step explanation:
Step: Solvex+y=7for x:
x+y+−y=7+−y(Add -y to both sides)
x=−y+7
Step: Substitute−y+7forxin2x−3y=−21:
2x−3y=−21
2(−y+7)−3y=−21
−5y+14=−21(Simplify both sides of the equation)
−5y+14+−14=−21+−14(Add -14 to both sides)
−5y=−35
−5y
−5
=
−35
−5
(Divide both sides by -5)
y=7
Step: Substitute 7 for y in x=−y+7:
x=−y+7
x=−7+7
x=0(Simplify both sides of the equation)
y = 7, x = 0