HELP! Calculating column total using VLOOKUP

[bendowse]

I am trying to use the VLOOKUP feature to calculate a total column. Here is roughly what i have:

A B C D E F G
- 1 2 3 4 5 6
a 2 3 4 5 6 7
a 3 4 5 6 7 8
a 4 5 6 7 8 9
- 5 6 7 8 9 10

a

basically i want to add up a column (eg E) only when the value has an "a" beside it. Can you please help me with the formula please?

 

[tactps]

=sumif(a:a,"a",e:e)