1 tire line. 305/45R18 tires sized to your wheels and your car.

A 305/45R18 is 305 mm wide with a 137 mm sidewall (45 series) on an 18 inch wheel, 28.8 inches tall overall. A tire size only makes sense next to a wheel width and a car. 305/45R18 mounts on a range of widths, and the overall height decides whether the speedometer and the fender stay happy.
1 line carries 305/45R18, from Nitto. By type that is 1 performance summer. 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 305/45R18 lines that do both.