Statistical Investigation

A newspaper sent a letter to 7500 persons in a town with the question "Do you agree with the decision to build a new football stadium in town?".

2100 people answered yes, 290 answered no and the rest didn't have any opinion. The newspaper took a random sample of 50 persons of the ones who didn't answer and it was showed that 22 said no, 8 said yes and 20 didn't know.

Calculate the percentage in favor of and against the decision

The right answer is:

In favor of: 31.9%

Against: 35.5%

I just need to know how to calculate it.