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. ([tex](-2,-3)[/tex]:
[tex]3(-2)-4(-3)=6[/tex]. This doesn't make the equation equal 21. So this isn't the correct answer.
B. ([tex](0,7)[/tex]:
[tex]3(0)-4(7)=-28[/tex]. This doesn't make the equation equal 21. So this isn't the correct answer as well.
C. ([tex](-3,-2)[/tex]:
[tex]3(-3)-4(-2)=-1[/tex]. This doesn't make the equation equal 21. So this isn't the correct answer also.
D. ([tex](7,0)[/tex]:
[tex]3(7)-4(0)=21[/tex]. This is equal to 21, so it makes the equation correct.
ANSWER: D
