The answer is fill its tanks with air so it floats to the top, but I will solve for the distance since I am nice
so we do decent means negative cimb=positive add
decends 45 and 1/2 -45 and 1/2
climbs 39 +39
decedns 18 and 3/4 -18 and 3/4
add -45 and 1/2+39-18 and 3/4 add convert 1/2 to 2/4 gropu negatives -45 and 2/4-18 and 3/4+39 add -63 and 5/4+39 -64 and 1/4+39 -25 and 1/4 that is how far dow the submarine is so the submarine needs to gu 25 and 1/4 ft up to reach the csurface