I need an excel formula to lookup values from different sources

I have a spreadsheet, and need to write a formula that looks up if certain drop downs are selected then it will total up the values on another sheet. It seems a little more complex than a basic vlookup or IF formula, but someone who knows will know!

The values are on the attached sheet - I need the first sheet cells in yellow completing, based on the examples on the "transactions" tab. A few mins for someone who knows!