So the first two line segments added together equals the full line segment. So, 8y + 5 + 7y = 13y + 25
15y + 5 = 13y + 25
2y = 20
y = 10
If the width is 15, and the scale factor from width to length is 3:2, then you will have to divide 15 by 3 to get your original width.
15/3 = 5.
5 is your original width.
25 feet above sea level means she travelled 25 feet to the surface of the sea. She would have to descend (37-25=12) 12 more feet to achieve 37 total feet of travel, so she descended 12 feet below sea level.