Answer:
x = 13
y = -5
Step-by-step explanation:
Let x = the first number
Let y = the second number
x + 2y = 3 2x + y = 21
You have two unknowns, so you need to equations to solve.
Solve the first equation for x:
x + 2y = 3
x = -2y + 3 Substitute this in for x in the second equation.
2x + y = 21
2(-2y + 3) + y = 21 Distribute the 2
-4y + 6 +y = 21 combine the y's
-3y = 15 Divide both sides by -3
y = -5
Plug -5 back in for either equation
x + 2y = 3
x + 2(-5) = 3
x -10 =3
x = 13
