AquaWorld is a full service dive shop based at the Park Royal in Cozumel. Dive shop management knows that its clientele possesses a diverse range of experience (or lack thereof) in diving. Some clients need a lot of hand-holding, prefer to follow a guide while under water, and usually rent their equipment. In contrast the more experienced divers tend to prefer to venture out on their own and generally use their own equipment. AquaWorld has effectively created packages with appropriate pricing for both types of customer. Apparently, AquaWorld is using a differentiated targeting strategy.

A3-mm-thick panel of aluminum alloy (k 177 w/m-k, c 875 j/kg-k and ? = 2770 kg/m) is finished on both sides with an epoxy coating that must be cured at or above t,-150°c for at least 5 min. the production line for the curing operation involves two steps: (1) heating in a large oven with air at ts,0-175°c and a convection coefficient of h, 40 w/m2. k, and (2) cooling in a large chamber with air at 25°c and a con- vection coefficient of he 10 w/m2.k. the heating portion of the process is conducted over a time interval te which exceeds the ime required to reach 150°c by 5 min (h = r + 300 s). the coating has an emissivity of ? = 0.8, and the temperatures of the oven and chamber walls are 175 and 25°c, respectively. if the panel is placed in the oven at an initial temperature of 25°c and removed from the chamber at a safe-to-touch tempera ture of 37°c, what is the total elapsed time for the two-step curing operation?