1 tire line. 275/55R21 tires sized to your wheels and your car.

275/55R21 means a 275 mm section width, a sidewall 55 percent of that (151 mm) and a 21 inch rim, which works out to 32.9 inches tall. Whether 275/55R21 works comes down to the wheel width it mounts on and how far it lands from the height the car left the factory with.
1 line carries 275/55R21, from Michelin. By type that is 1 highway. The tire has to stay near your car's stock height and mount on your wheel width, so pick the car and the wheel set and the page keeps only the 275/55R21 lines that do both.