Hi.
To solve this problem, we have to multiply the depth of the ocean at the lowest point by 1/50. To put it another way, we have to divide the depth of the ocean by 50:
2.78 x 104 feet x 1/50 = 2.78 x 104 feet / 50
The scuba diver dove 556 feet.
By the way, this is deep enough that the diver, on her ascent, would need to make decompression stops in order to avoid the dangerous condition called "the bends!"