First, make a diagram to visualize the problem. I have made drawn the diagram in the attached image. As you can see, there are 2 variables x and y. x denotes the depth of Hailey while y denotes the distance between Hailey’s diving partner and the boat. We solve first for x.

Since it is a right triangle, we use trigonometric functions like tangent. With respect to the angle, tangent is the opposite side over the adjacent side. So,

tan 30 = x/300
x = 173.21 ft

Now, looking at the outer triangle, you want to find y which is the hypotenuse. The equation would be:

y = √[300² + (x+25)²]
y = √300² + (173.21 +25)²
y = 359.67

Thus, the distance is 360 feet.