The hour hand advances between individual numbers as the minute hand makes a full path around the hour. The hour hand was pointing directly at 3 at 3:00, but at 3:15 it has advanced 1/4 of the way between 3 and 4. The number of degrees between numbers 30 (because 360/12). That gives you 30/4 = 7.5. The number of degrees between the two hands is 7.5 degrees.
The hour hand advances between individual numbers as the minute hand makes a full path around the hour. The hour hand was pointing directly at 3 at 3:00, but at 3:15 it has advanced 1/4 of the way between 3 and 4. The number of degrees between numbers 30 (because 360/12). That gives you 30/4 = 7.5. The number of degrees between the two hands is 7.5 degrees.