I would be really grateful if someone could offer some assistance.

I am in the process of creating a time recording spreadsheet. I have
formatted cells B5:B9 using the time cell format: HH:MM. In cell B10 I wish
to have a calculation which will total the number of hours worked. How do I
do this?

I find the problem is that if I were to add 03:45 and 00:30 this would come
to 03:75 instead of the required result of 04:15.

I'd be really grateful if someone could offer some help of advice.

Many thanks,

Simon.