The average age of 39 students in a group is 14 years. When teacher's age is included to it, the average increases by one. What is the teacher's age in years ?  Choose the correct choice from the following choices.
A) 35 years
B) 45 years
C) 51 years
D) 54 years
E) None of these
Explanation:   Age of the teacher = (40 * 15 - 39 * 14)= 
<gadget id="calculator">(40 * 15 - 39 * 14)</gadget>
<output>54</output>
54 years. Answer: 54 years
<result>D</result>
The average age of 39 students in a group is 14 years. When teacher's age is included to it, the average increases by one. What is the teacher's age in years ?