After a surface interval, you are a D diver. You wish to make a dive to 42 feet. What is your Residual Time (RT)?

To determine the Residual Time (RT) for a diver at the depth of 42 feet, it is necessary to consider the last dive depth, the total bottom time, and the subsequent surface interval. The RT is the amount of time that must be counted as residual from the first dive before an additional dive can be made safely.

Given that you're at a depth of 42 feet as a D diver, specific tables or algorithms would typically provide the residual nitrogen time needed based on the previous dive profile. In this instance, the chosen answer indicates that the RT calculated reflects the known values within the guidelines for safe diving.

The RT of 29 minutes corresponds with the appropriate calculations and guidelines for a diver making a subsequent dive. This would ensure that the diver minimizes the risk of decompression sickness by allowing for adequate off-gassing.

In contrast, the other responses would suggest a misunderstanding of safe residual times or inadequate calculations based on potential nitrogen saturation levels. Thus, the value of 29 minutes is rooted in ensuring a safe transition from the surface interval to a new dive at the specified depth without exceeding safe limits for residual nitrogen in the body.