1. Radius of 8 cm = ------------------------ diameter
2.Radius of 3.75 ft =------------------------diameter
3. Radius of 11.2=-----------------------------diameter
Note that the third one doesn't have a unit of measurement. Was that an oversight?
Note that diameter = twice the radius. Thus, if the radius is 3.75 feet, the diameter is twice that, or 7.50 feet. Can you now do the other two problems?