Help with Excel

Basically i have did this up as a test before i do the proper one

i will have multiple tabs on the bottom for customers / suppliers etc
on the left is week 1 to 52
on the top are services we will offer and unit rates etc

i want to be able to input weekly figures ( unit rate will stay same ) but quantities will vary , but i'd like it to add the figures to the master sheet ( pic 2 )

so tabs will be like

master / customer 1 / customer 2 / customer 3 / etc

if they all use a certain service lets say packing , i want to be able to see overall how many units of packing was charged out

but no idea of what formula ( excel novice ) could somebody do something for me id be very grateful