4x+4y=12 and x-7y=-21 solve by substitution

Question

I dont understand how to solve by substitution.

Answer 1

Substitution method

Given equations are 4x+4y = 12 ---> (1)

x-7y = -21

Add 7y  to each side.

x+7y-7y =-21+7y

x = 7y-21 ---> (2)

From (2) substitutethe x value in (1).

4(7y-21)+4y = 12

28y-84+4y = 12

32y-84 = 12

Add 84 to each side.

32y-84+84 = 12+84

32y = 96

Divide to each side by 32.

32y/32 = 96/32

⇒ y = 3

Substitute the y value in equation (1).

4x+12 = 12

Subtract 12 from each side.

4x+12-12 = 12-12

4x = 0

Divide to each side by 4.

4x/4 = 0/4

⇒ x = 0

Solution x = 0, y = 3.