Erika has 6 red pens, 9 green pens, and 10 black pens in her pencil case. Erika randomly picks one pen from the case, writes down the color, and puts the pen back. If she repeats the process 100 times, which is the best estimate of the number of times she should expect to draw either a red or black pen?
A. 76%
B. 24%
C. 64%
D. 60%