An object of height (5.00±0.05)cm is placed (28.0±0.2)cm in front of a concave mirror. The virtual image is measured to have a height of (9.00±0.10)cm. Which of the following best represents the focal length of the mirror with its absolute uncertainty?
a) f=(18±2)cm
b) f=(63±2)cm
c) f=(31±2)cm
d) f=(63±6)cm