The answer is 10 people. The way you know is because the surveyor asked the person for one answer, so if you results were 1, 0, ,10 ,7 ,13 ,2 ,9,15 ,0 and 3, then obviously only 10 people were asked because you have 10 answers.
The area of a circle is equal to the radius squared times pie, basically:

The radius is 3, so we multiply 3 times 3 times pie to get the area.
You're gonna want to plug in the following into a calculator:

After getting 28.26 from such calculator, you need to round to the tenths place. In this number, the tenths place is the 2 next to the decimal on the right. Because the number after the 2 is a 6, that means we need to simplify the answer to (28.3). When you are rounding a number, you look at the number to the right, if it is 5 or bigger, add one and remove the rest, if it is less than 5, just get rid of the rest and leave it as it is.
The most simplified version would be: