1. The problem statement, all variables and given/known data A magic stalk starts growing at a spot 10 metres from a 4 metre lamppost. The stalk grows 1 metre per hour. Find the rate at which the length 's' of the stalk's shadow is increasing at the instant when the height h of the stalk is 3 metres. 3. The attempt at a solution First, I drew a diagram, 4m lamppost as left edge of a triangle, 3 metre height in the middle of the triangle, and 10+s base (10 meters from the beanstalk to the lamppost, and length 's' shadow. I know this part is right. After this, I'm lost as to what I should do. I think it might be something with c^2=a^2+b^2, but the two equations seem to get very complex, so I must be doing something wrong, and I have no idea how I would combine them. (after which I assume I need the f'(x), because f'(x)=v'(t)=1, but really have no idea? So any help in the right direction would be highly appreciated. Thanks.