To calculate the diver's current depth, we need to subtract the ascents from the descents.
The diver started at sea level, then descended 42 feet below sea level, which gives us -42 feet.
The diver then ascended 18 feet, so we add that to the current depth (-42 + 18 = -24 feet).
Finally, the diver descended 7 feet, so we subtract that from the current depth (-24 - 7 = -31 feet).
Therefore, the diver's current depth is 31 feet below sea level.
The correct response is: 31 feet below sea level.