The hour hand moves at 1/2° every minute
The minute hand moves at 6° every minute
Using the top of the clock as 0°.....at 12:25
The minute hand has moved 25 * 6 = 150° from the top of the clock
The hour hand has moved 25 * 1/2 = 25/2 = 12.5° from the top of the clock
So.....the angle between them is 150 - 12.5 = 137.5°