Answer:
Adding 3x each time
Step-by-step explanation:
To find the difference, subtract the 1st value from the 2nd; 2nd value from the 3rd;.........
(6x + 3)=1st value
(9x + 3)=2nd value
(12x + 3)=3rd value
9x+3-(6x+3)
9x+3-6x-3
9x-6x=3x
Check
6x+3+3x
=9x+3
12x+3-(9x+3)
12x+3-9x+3
12x-9x=3x
Check
9x+3+3x
=12x+3
