Just listen to what Prime is telling you!
If Prime says that the units are not compatible, thats usually true and you should check either the units assigned to your variables or your equations (or both).
Obviously you can't add or subtract quantities of different dimensions.
You try to subtract J and J/kg. This can't work.
So check your units, check your formula!
For further question please don't send just pictures or pdfs - attach your worksheet!
