Question

a boat heads directly across a river with a speed through the water 8m/s. the river current is 2m/s a. what is the magnitude and direction of the boat velocity relative to the earth?
b.when the boat reaches the other bank, how far will it be?

Answer 1

draw the velocity vectors. The resultant speed has magnitude v=√(2^2+8^2)
It drifts downstream by an angle θ such that tanθ = 2/8

without knowing the distance across the river, it's hard to say how far downstream it will have drifted. Also, you don't define exactly what you mean by "far."