This is a PERT (Program Evaluation and Review Technique) estimation problem. The formula used is: Expected Duration (TE) = (Optimistic + 4×Most Likely + Pessimistic) / 6 = (5 + 4×11 + 20) / 6 = (5 + 44 + 20) / 6 = 69 / 6 = 11.5 # Rounded = 12 days While 11.5 is the exact mathematical output, PMI-style questions typically round this to the nearest whole number when appropriate. Thus, the correct answer is C. 12 days References: PMBOK Guide - Seventh Edition, Planning Performance Domain PMI Practice Standard for Scheduling