Taking a value from another sheet and multiplying (cost x hours) and combining days, weeks

Hello everyone,

I have tried to make a sheet which has

Resource, Task, Rate (I'd like this to be on another sheet, as it does not help here and is a lot of repetition)
Also, right now the columns for hours are based on weeks, but i'd like to do it by days and then collapse by weeks, and months and get totals by weeks and months too. I have no clue how to do that.
Then, I'd like to multiply the rate by the hours to find the total number of hours, however the way it is done right now is not very intelligent and very time consuming when creating the formula, which looks something like this =SUM(H4*$C$4,H5*$C$5,H6*$C$6,H8*$C$8,H9*$C$9,H10*$C$10,H11*$C$11,H13*$C$13,H14*$C$14,H15*$C$15,H16*$C$16)

Can you please give me some pointers as to what can be done to make this a bit better?

Thanks,
G