How do I find the height of the image?

[phys62]

Homework Statement

A 1.80-cm-high object is situated 19.7 cm in front of a concave mirror that has a radius of curvature of 12.2 cm. Calculate (a) the location and (b) the height of the image.

Homework Equations

f=1/2R
1/image distance + 1/object distance = 1/f

The Attempt at a Solution

f=1/2(12.2) = 11.1
1/image distance + 1/19.7 = 1/6.1
image distance = 8.836 cm

then I thought to find the image height I'd just take 8.836 cm - 1.8 cm = 7.036 cm but this is incorrect.

 

[jambaugh]

The ratio of image height to object height = the magnification will equal the ratio of distance from image over distance of the object to the mirror or lens.