The drawing shows a circle, with the two lines forming a cross assumed to be perpendicular to each other, so this is most likely to be a square, as the four points at which the perpendicular lines intersect with the circle can be connected to form a square.
We would need 3 points for an equilateral triangle, 5 for a pentagon, and 6 for a hexagon, which do not fit the current steps.
Sara's results probably do have a higher mean, if we take into account how William is way more willing to pay 20 dollars. Honestly, I think you got your chosen answers right! Just my opinion, as someone inexperienced.
3 in the power of ten means "10^3."

How to solve exponents is to multiply the number as many times as it's exponent. So in this case you will have to multiply ten, three times.

Which would mean that....

The answer is 10^3.
Hope this helps.