Excel formulas. Do not use solver.

An operations manager claims that one of the production processes he oversees has a learning rate of 88%. One of the new components produced in this production process has the following completion times in minutes) for the first five units: 55, 45, 40, 37, and 35: a (3 points) Is the manager's claim of an 88% learning curve valid? Support your answer with appropriate calculations. b (2 points) If the manager's claim is not valid, what is the correct learning rate