Can someone help me with this.

A good place to start would be to draw the circle and the rectangle. Then notice the relationship between the diameter of the circle and the diagonal of the rectangle.

See where you can go from there. If you get stuck, please reply showing (or describing) what you have tried. Thank you.

Eliz.

Okay, so you have a rectangle inside a circle. You've labelled the diameter. You've labelled the height and width of the rectangle.

Then what? What have you done with the lines I suggested? What relationships have you looked into?

Please be specific. Thank you.

Eliz.

That last part is the part I don't understand. I don't know what to do, is there a formula I could use?

Appears to me you're not aware of this:
if a rectangle is inscribed in a circle, the 4 corners are on the circumference,
and the diameter of the circle is the diagonal of the rectangle.

Denis,
I am aware of this................ can you help me?

You haven't shown us what you've tried, so we can't tell where you're having trouble. Do you not know the formula for the area of a rectangle? Have you not studied anything to do with right triangles?

We gave you instructions; you said you'd gotten that far but could do no more. We gave you more instructions; you said you'd gotten that far but could do no more. We gave you hints; you said you'd gotten that far but could do no more.

This looks a little odd. Please reply showing your work and stating clearly where you are stuck. Thank you.

Eliz.