For the slope, you'll need to do implicit differentiation using the chain rule. Are you aware of how to do that?
For the related rates, we are told that
I'm not certain at first glance whether it should be negative but I'm going to go with that for now. I'll think about it and correct in a few mins if I decide it should be something else.
We can deduce that the height of the triangle will be using Pythagoras. The area of the triangle will be using the fact that 'area is half base x height'
This means that we can find
Then use the chain rule:
I'll leave part b) for now until we've covered what's here so far.
Hope it helped.