Finding the Time and Cost from the Given Data

"Suppose that a learning curve us described by the function T(N) = 20/√N Where (T)n is the time in hours to produce the nth unit. a. How much time is required to produce the fourth unit. b. How much time is required to produce the first four units. c. If the cost of labor is $10 per hour, how much money does if cost the to produce the first four units. "