Draw a line of 8 carbons, and join them by single bonds. This isthe backbone of your molecule, the octane part. Now draw lines torepresent the rest of the bonds on the backbone, one above and onebelow each carbon, and one more at each end ( a total of 18).Imagine the carbons numbered from the left (you could use theright, but you have to pick one.) Put a CH3 group above each ofcarbons 2, 3 and 4. Put a C2H5 group below carbon 4. Add an H atthe end of each empty line. Now check: you should have a total of13 C's and 28 H's.