Foreign Tax Credit Computation Worksheet

I'm a US citizen living and working in South Korea. I paid Korean local and federal income taxes out of my paycheck. I have a Korean bank account and also have a mutual fund back in America that reported foreign taxes paid on a 1099-DIV.

 

I'm trying to file my tax return. Turbo tax says the following items need fixing, and I don't understand the information it's asking. 

 

Line 4b2c: Adjusted basis for total business assets

Line 4b3c: Adjusted basis for total passive activity assets

Adjusted basis of total investment assets
 
I put zero into these boxes, because I'm not familiar with this terminology and it seems like it wouldn't pertain to me. But TurboTax says the number must be larger than zero. Does anyone have a suggestion of how to find the correct number?