disp(['The approximate work done is: ',num2str(W),' kJ'])
The way I personally approach constructing things like this is to first write out the sentence without using the variable:
disp(['The approximate work done is: 123 kJ'])
then isolate the numeric piece, using concatenation:
disp(['The approximate work done is: ','123',' kJ'])
and then substitute in the num2str as above.
