Max error and relative error

The circumference of a sphere was measured to be http://webwork.asu.edu/webwork2_file...63e9778881.png cm with a possible error of http://webwork.asu.edu/webwork2_file...5b5ed35541.png cm. Use differentials to estimate the maximum error in the calculated surface area.

Estimate the relative error in the calculated surface area.

This is what i tried but i got it wrong?

Circumference of a sphere = 2πr

so r = 11.61831

SA=4πr^2

SA=1696.2731

SAmax=1845.4147

Maximum error = 149.1416 ? this is wrong

Relative error = change in SA / SA

f'sa = 8πr so change in SA = 8π(11.61831)(.5) = 145.9999

relative error = 145.9999/1696.2731 = .08607

can i get some help with what to do because i guess i am doing it wrong (Crying)

thank you