$$A scuba diver makes a slow descent into the depths of the ocean. His vertical position with respect to a boat on the surface changes several times. He makes the first stop $9\mathrm{.}0$ m from the boat but has a problem with equalizing the pressure, so he ascends $3\mathrm{.}0$ m and then continues descending for another $12\mathrm{.}0$ m to the second stop. From there, he ascends $4$ m and then descends again for $24\mathrm{.}0$ m$,$ where he makes a stop, waiting for his buddy. Assuming the positive direction up to the surface, express his net vertical displacement vector in terms of the unit vector. What is his distance to the boat?