Distance Between Two Cargo Ships Ship A leaves port sailing north at a speed of 20 mph. A half hour later, Ship B leaves the same port sailing east at a speed of 35 mph. Let t (in hours) denote the time ship B has been at sea. (a) Find an expression in terms of t giving the distance D between the two cargo ships. D(t) = (b) Use the expression obtained in part (a) to find the distance (in miles) between the two cargo ships 4 hr after Ship A has left port. (Round your answer two decimal places.) mi