Answer= (7,0)
For the sake of clarity, I'll try and solve for all the ordered pairs
(-2,-3)
3a-4b=21
3*-2-4*-3=21
-6+12=21
6≠21
(0,7)
3a-4b=21
3*0-4*7=21
0-28=21
-28≠21
(7,0)
3a-4b=21
3*7-4*0=21
21-0=21
21=21
Correct
(-3,2)
3a-4b=21
3*-3-4*2=21
-9-6=21
-15≠21
