precious

I got in precious this morning to make a run to town to find that she was sick. She was running rough so, I got to the end of the street and turned around to head back to the garage and the chk engine light came on. My husband had it checked and it coded a misfire on cylinder 4. The car has 80k+ and the original plugs look good. Wondering if it could be the coil and if so, how can you check to see if the coil is bad before I make a $80 mistake. Thanks