I do not know where to start.

You can set up a proportion and solve it by cross-multiplying:
8.9% = 1,100
100% = x

8.9x= 110,000
x=12,359

This particular problem can also be easily solved if you think of it this way: since 8.9% or approximately 10% of the total is 1,100, then total will be a little more than ten times 1,100 or just over 11,000.

If you round off 8.9% to 9% and then calculate

9%=1100

100% will be around 12000,

the c answer fits it.(it takes less than 1 min)

Cheers

agree that rounding to 9% is a good idea. another quick tip could be to know that 100%/9% approx equals 11, so you can just multiply 1100 by 11 to find a close approximation of 12100.
So C is answer