time card I have to calculate by the 10th of the hour

Here is the situation. I spend over 3 hours manually calculating time cards and I want to create a excel program that can quickly and easily add the hours for me. If anyone can help please read the details below and let me know how I can do it!

If I look at a time card I have to calculate by the 10th of the hour

Example: John Smith works
9:00a - 12:00p and then 12:31p 4:30p

I need excel to translate that to 3.0 hours and 3.9 hours = 6.9 hours

10th of the hour calculator

0-5 mins = .0
6-11 mins .1
7-17 mins .2
18-23 mins .3
24-29 mins .4
30-35 mins .5
36- 41 mins .6
42-47 mins .7
48-53 mins .8
54-59 mins .9
1 hour = 1.0

Please help

Hi,
try

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and format as number ( a2 is the end time and a1 the start time)