What does it mean by the angle "with the vertical?". If it's #80^"o"# clockwise or anticlockwise from the positive#y#-axis, then this makes no sense as the raindrops appear to be going upward on the windows. Does it want #80^"o""# from the negative#y#-axis? Then the angle is #-10^"o"#, which is much more logical, as it is traveling down the car's window.