labour efficiency ratio

A hotel has 120 identical bedrooms. It uses labour efficiency percentages to compare the performance of four groups of workers (A, B, C and D) employed to clean the bedrooms. The standard time to clean a bedroom is 40 minutes.

The following data for last week are available:

Group A actual hrs worked- 128 actual #of bedrooms cleaned – 198
B actual hrs worked- 140 actual #of bedroom cleaned- 207
C actual hrs worked- 124 actual #of bedroom cleaned- 186
D actual hrs worked- 108 actual #of bedroom cleaned- 165

it says that the correct answer is group A for most efficient, but they didn’t show the solution..

the formula for labour eff. ratio is standard hrs for actual output/actual hrs worked*100

if im gonna get for group A is this solution correct .. 0.66*198/128*100?
and 0.66 came from 40minutes/60minutes