You can find it easily by just counting the number of squares inside the square, or by counting the number of squares at its length then multiplying it by its width; so 3 x 3 = 9
It wouldn't be as easy to find the area of the circle because you don't have the radius, nor diameter, so basically, no quantitative values could be used to at least guess.
The area of the square is 3 units by 3 units. because the area of a square is side length squared.
side length = 3
side length^2 = 3 * 3 = 9
The area of a circle is much harder to reason out. You could start with the area of a square and use the diameter is 3 units. But the corners are rounded and you don't know off hand what the area of one of them is, let alone all 4. You are given a formula for circles area, but you have no real idea what the formula actually means. Does it take the corner area into account? At the beginning levels, we don't know.
Assuming that the side of the triangle marked 13.5 is tangent to the circle, the there's a right angle where the radius meets the tangent segment. The triangle is then a right triangle and the Pythagorean Theorem applies.
