Which value of x satisfies both -9x + 4y = 8 and -3x − y = 4 given the same value of y?

Question

A.-1/7
B.-7/9
C.-8/7
D.-9
E.-4/3

Answer 1

This prolblem is quickly solved with the elimination (also called addition/subtraction) method

Multiply the second eqution by 4

-12x - 4y = 16

Now add that to the first equation

-9x + 4y = 8

-12x - 4 y =16

This sum is -21x = 24

Divide both sides by -21 and you get x= -24/21 which reduces to -8/7

Answer C