determine the estimated uncertainty for the area of circle with a radius of 10.45+-0.5cm
I assume that you have not done calculus before.
To find the uncertainty, calculate the area of the circle when the radius is the maximum possible, minimum possible, and the given radius, i.e. r=10.45+0.5cm, 10.45-0.5cm, and 10.45 cm. to give A2, A1 and A respectively.
The maximum uncertainty is the larger of (A2-A) or (A-A1).