Find, add and return values from multiple tables.

Hi, Hope someone can assist.

I am looking for a solution to the following (I will use the attached document as an example but have a much larger document to work with in real terms):

If I had the following three tabs each tab has the same individual however the order they study subjects or what subject they study per week can differ.
On tab 4 I would like to be able to add all three. for example Adam spends in total studying science a value of 7 - Tab 1 - Science = 1, Tab 2 - Science = 4, Tab 3 - Science = 2. So tab 4 I would want Science = 7 and then also all the other subjects he studies and from week to week this could vary.

I was thinking either some kind of SUM IF statement maybe some kind of IF(Vlookup)? Or I've seen a little of INDEX forumas around if that could be a method. OR would Pivot tables be a way to go, though I can't seem to get my head around producing a pivot table for something like this.