Question

Solve systems by substitution method x + y = 20 3x + 4y = 72

Answer 1

X=-12 and Y= 32

Explanation:

x+y=20 -> 1

3x+4y=72 -> 2

Form 1,

[x+y=20]×4

4x+4y=60 ->3

Form 2,

3x+4y=72

4y= 72 -3x ->4

Sub (4) into (3)

4x+72-3x= 60

x = -12

Sub X=-12 into (1)

-12+y=20

y= 32

Hope this helps.

Answer 2

x = 8; y = 12.

Explanation:

x + y = 20

x = -y + 20

3x + 4y = 72

3(-y + 20) + 4y = 72

-3y + 60 + 4y = 72

y = 12

x + 12 = 20

x = 8

Check your work!

3(8) + 4(12) = 72

24 + 48 = 72

72 = 72

Hope this helps!