There are probably other, simpler ways of doing this, but before excel I was using spreadsheets to keep the sums of my logbook accurate, and continued this way when excel became the spreadsheet to use. It is quite simple (I think!)
Hours and minutes are entered in cells using a decimal format, so two hours and fourty minutes is entered as 2.4 and let's say you entered it in cell A1. Now by use of the following formula, it is converted into real decimal hours, so you bung into another cell:
=INT(A1)+(A1-INT(A1))/0.6 this should make this cell read 2.666667 which is the decimal hours of 2 hours 40 minutes. Now you can do what you like with this, multiply it by an hourly rate or add it to another similarly decimalised hours.minutes entry (as I do). Should you then wish to turn the answer into hours and minutes again in an hours.minutes format, the process is reversed by using the formula =INT(A1)+(A1-INT(A1))*0.6 where again cell A1 is the cell where the decimal hours which require their format converting reside.
I expect that there is a much simpler way of doing this in excel, but it is the way I understand because I have always used it since the days of supercalc and DOS. It works for me!
P.P.