If you traveled via vehicle, you should not enter the car expenses in that spot. Enter the lowest return airfare for the destination. Enter the actual expense amount from traveling via vehicle in the spot marked "Travel Expenses".
CRA requires that information as the calculation for the allowable amount has to be the lesser of these three amounts:
http://www.cra-arc.gc.ca/tx/ndvdls/tpcs/ncm-tx/rtrn/cmpltng/ddctns/lns248-260/255/clc-eng.html
If you traveled via vehicle, you should not enter the car expenses in that spot. Enter the lowest return airfare for the destination. Enter the actual expense amount from traveling via vehicle in the spot marked "Travel Expenses".
CRA requires that information as the calculation for the allowable amount has to be the lesser of these three amounts:
http://www.cra-arc.gc.ca/tx/ndvdls/tpcs/ncm-tx/rtrn/cmpltng/ddctns/lns248-260/255/clc-eng.html