Hi haftakhan,

Fori, I got this:

Area of big circle:

Area of small circle:

Area of shaded region:

The perimeter of the circle with radius 10:

The perimeter of the circle with radius 6:

The combined perimeter of the shaded region:

Forii, I got this:

Area of circle:

Area of Square:

Area of shaded region:

The perimeter of the shaded region:

Foriii, the area looks good, but I don't see how you got 75 for the perimeter.

I haven't looked at the others, but if you want to post them individually and show how you got your answers, that'd be good.