Is this right? Please help me

The midpoints of the sides of the large square are joined to form a smaller square. what is the area of the smaller square

You are standing next to a really big circular lake. you want to measure the diameter of the lake, but you don't want to have to swim across with a measuring tape! you decide to walk around the perimeter of the lake and measure its circumference, and find that it's 400\pi\text{ m}400? m. what is the diameter dd of the lake?

What is the sum of the measures of the interior angles of an octagon