Answer: 0.5263
Step-by-step explanation:
Given : The completion times for a job task range from 11.8 minutes to 19.4 minutes .
The density function for uniform distribution function for interval [a,b] :-

Then the density function for the given situation:-

The required interval : 
Now, the probability that it will require between 12.8 and 16.8 minutes to perform the task will be :-

Plant C, because it shows at the thirty day mark that they have the highest production rate.
Cos A = adjacent/hypotenuse
Cos A = 9/26 = 0.346