Answer:
B) 9
Step-by-step explanation:

x = 9
Proportionality, assuming constant rate. 460 dives/12 hours = x dives/3 hours. Solve for x.
= 3/5(x) + 3/5(x) + 2/5
= 6/5(x) + 2/5
= 2/5 (3x+1)
I hope that is what you are looking for.
The diagonal is the hypotenuse of a right triangle with the sides of the square as legs.
By Pythagoras (s = side)
s^2 + s^2 = 15^2
2s^2 = 225
s^2 = 112.5
s = sqrt(112.5)
s = 10.6 cm (to the nearest tenth)