Question

Which expression can you substitute in the indicated equation to solve the system below?

9y = 6 - x
12x = 5 - y

A. Substitute 5 - x for y in to 9y = 6 - x
B. Substitute 6 - 9y for x in to 12x = 5 - y
C. Substitute 5 + 12x for y in to 9y = 6 - x
D. Substitute 6 + 9y for x in to 12x = 5 - y

Answer 1

B. Substitute 6 - 9y for x in to 12x = 5 - y

Explanation:

From the first equation we solve for x and get

x = 6 - 9y.

and one way to solve the given system of equations is to put this value of x into the equation 12x = 5 -y. this will give us 12(6 - 9y) =5-y, which can be easily solved for y.

Therefore choice B is the correct option.

Let us go through other choices for the sake of completeness

Choice A gives the wrong value of y for substitution.

Choice C also gives the wrong value of y for substitution.

Choice D gives the wrong value of x for substitution.