Question

A system of linear equations is given as x + 3y = 36 and 4x + 5y = 9. Which of the following is a possible first step when solving by substitution? *

1 point
Rewrite the first equation as x = 36 – 3y.
Rewrite the first equation as y = 1/3x + 12.
Rewrite the second equation as x = 9 – 5/4y .
Rewrite the second equation as y = 9 + 4x.

Answer 1

Rewrite the first equation as x = 36 – 3y.

Explanation:

x + 3y = 36 (1)

4x + 5y = 9 (2)

Using substitution method

From (1)

x = 36 - 3y

Substitute x = 36 - 3y into (2)

4x + 5y = 9

4(36 - 3y) + 5y = 9

144 - 12y + 5y = 9

- 12y + 5y = 9 - 144

-7y = -135

y = -135 / -7

y = 19.3

There is an error with the second equation, 4x + 5y can not be equal to 9

Nevertheless, the first step when solving by substitution is:

Rewrite the first equation as

x = 36 – 3y.