Aptitude test preparation

At what time between 4 and 5, will the hands of a clock coincide? (Answer in minutes up to 2 decimal places)
for this Q i have solved using every formula and technique yet i am getting the same ans- 21.81 and it is showing incorrect when i try to submit the following answer. can u pls tell the correct ans for the above mentioned Question!!!

Did you round it first and then checked it??