To find the measure of the angle of the pizza that Johnson ate, we first need to find the angle of one piece of the pizza. Since Johnson cut the round pizza into 12 equal pieces, we can calculate the angle of one piece as follows:
The total angle in a circle is 360°. Therefore, the angle of one piece is:
\[ \text{Angle of one piece} = \frac{360°}{12} = 30° \]
Since Johnson ate 4 adjacent pieces, we can calculate the total angle he ate as follows:
\[ \text{Total angle} = 4 \times \text{Angle of one piece} = 4 \times 30° = 120° \]
So, the measure of the angle of the pizza that Johnson ate is 120°.