* Convert to the same units: Since one measurement is in centimeters (cm) and the other is in millimeters (mm), we need to convert them to the same unit. There are 10 millimeters in 1 centimeter.

* Convert 7 cm to mm: 7 cm * 10 mm/cm = 70 mm

Now we can compare:

* 70 mm (7 cm) is longer than 64 mm.

Therefore, the 7 cm pencil is the longest.