For the left side, first distribute:
14xz - 21yz = 7z * (2x - 3y)
Now, put this back into the equation:
7z(2x - 3y) = az(2x - by)
As we can see, the 7 on the left side corresponds to the a on the right side. The 3 on the left side corresponds to the b on the right side. So, a = 7 and b = 3, and a + b = 7 + 3 = 10.
The answer is 10.
