Question

Which ordered pair in the form (a, b) is a solution of this equation? 3a – 4b = 21

Answer 1

Plug in all the 4 answer choices with the first number in place of a and second number in place of b. Whichever makes the equation correct, is the right answer. Let's try all four.

A. ($(-2,-3)$:

$3(-2)-4(-3)=6$. This doesn't make the equation equal 21. So this isn't the correct answer.

B. ($(0,7)$:

$3(0)-4(7)=-28$. This doesn't make the equation equal 21. So this isn't the correct answer as well.

C. ($(-3,-2)$:

$3(-3)-4(-2)=-1$. This doesn't make the equation equal 21. So this isn't the correct answer also.

D. ($(7,0)$:

$3(7)-4(0)=21$. This is equal to 21, so it makes the equation correct.

ANSWER: D