Answer:
The answer is a. 14.33.
Explanation:
We apply the net present value (NPV) methodology to approach the two options.
+ The lifetime subscription's npv = $(850)
+ The annual subscription's npv = - 85 - [ 85/6% * [ 1 - 1.06^(-n) ], with n is the number of years the subscriber still lives.
To make a lifetime subscription a better buy, the NPV of this option should be higher than the NPV of annual subscription or:
85 + [ 85/6% * [ 1 - 1.06^(-n) ] > 850 <=> 1 - 1.06^(-n) > 0.54 <=> 1.06^(-n) < 0.46 <=> -n < -13.33 <=> n > 13.33.
So, the subscriber should live more than 14.33 years ( 13.33 + 1 years for another next year subscription) to make the lifetime subscription a better choice.
So, a is the correct choice.