A building contractor specializes in building homes for a developer who creates subdivisions with equally-sized lots. The contractor has determined from past projects the number of hours required for plumbing work, X, is a random variable with mean 32.8 hours and standard deviation 2.1 hours. The number of hours required for concrete work on the driveway of the homes, Y, is a random variable with mean 18.5 hours and standard deviation 1.2 hours. The contractor has determined that the plumbing costs and concrete labor costs are independent. What is the standard deviation of the total number of hours for plumbing and concrete work for these types of homes? (Round your answer to 2 decimal places.)