3a - 4b = 21
check (-2 , -3)
3(-2) -4(-3) =21
-6 +12 = 21
6 does not = 21 so NO
check (0 , 7)
3(0) -4(7) =21
0-28=21
-28 does not equal 21 so NO
check (-3 , -2)
3(-3) -4(-2) =21
-9 +8 = 21
1 does not = 21 so NO
check (7 , 0)
3(7) -4(0) =21
21 = 21
Choice D