VLookup Formula Help

Hi Guys,

Bit of an newbie here so here goes!

I have attached a sample spreadsheet which has Cable Types in Column A and Cable Length of said cable in Column B.

What I would like is to have a formula that will search Column A for the cable types get the corresponding length in Column B and sub-total them together in the red cells

I was thinking some sort of VLookup but cannot seem to get it quite right

Any suggestions would be appreciated!