A: The right triangle formed by point C and B and point (1,63) is similar to the one formed by C, A and point 2,63 by doubling the sides. That implies that the slope of CB is the same as the slope of CA.
B: The initial value at t=0 tells us that the shark is initially at a depth of 63 meters and is diving at a constant rate of (105-63)/1= 42 meters per minute.