300
The circumference for the circle dan drew on the board!
10(pi)!!! Since diameter is twice the radius, you know that r=5! After that, just plug n' chug, gitt 'r dunn!
C=2(pi)r
C=2(pi)*5
C=10(pi)!
Alternatively, if you knew that Circumference also equals Pi*Diameter, you can just go straight to 10*pi!!