physics #3?

Question

if the boat moves directly upstream relative to the water of the river of my previous question which was (a straight river with parallel banks flows at 4km/h. a boat moves directly downstream relative to the water at 11km/h. the velocity of the boat relative to the river bank is...?) at 9km/h, its velocity relative to the river bank is now...?

Answer 1

Summing vectors

V1 = 4 km/h downstream or -4 km/h upstream
V2 = 9 km/h upstream

Vres = V1 + V2