Look at the circle divided into 12 parts that represents a clock
Let's take each part as x°
we know that 12x°=360
x°=360/12
x°=30°
Now, how many parts are there between the hands of a clock at 8:00?
4 parts, which means
4x°
Replace x°
4*(30°)=120°
The measure of the smaller angle between the hands of a clock at 8:00 is 120°