Sum of wages for the year with varying start dates

I have a column of months (A) and a column of wages (B) corresponding to the start month of new recruits and their wage.

How do I sum up the total for the year ?

Example:
Start date:Jan in Column A, Wage 100 in Column B
Start date:Oct in Column A, Wage 150 in Column B

That would equal a total wage cost in the year of (100*12)+(150*3)=1650

I cant seem to work out a formula. My months come from a dropdown list, wages are whatever the user types into the cell next to the dropdown list of month.

Is that clear, or should i give up for Friday ?

Here is the example. Cheers

Ah ha, I see, that works well using the Index function.

Thanks for that, have a good weekend.