Question

Points C and D are directly across from each other on opposite banks of a river. A boat travels across the river directly from point c to point d at a speed of 12 mph. If the current of the river has a speed of 4 mph, at what angle, and speed, must the captain head to travel directly from c to d?

Answer 1

he needs to head upstream at an angle θ (measured from the line CD), such that

tan θ = 4/12
so, θ = 18.4°
The speed required is √(16+144) = 12.65 mph