Studying for a test, and have a few questions I'm confused about... Some of them are probably really easy, I just can't seem to get them right.

1. Find $\displaystyle \frac {dy}{dx}$ if $\displaystyle x^4 +2x^2y^3 + y^2 = 21$

2. Differentiate $\displaystyle y = \sqrt \frac {x}{(1 + x^2)} $

3. A spherical balloon is being inflated. If the volume of the balloon is increasing at a rate of $\displaystyle 10 m^3/min$, how fast is the radius increasing when the radius is 3m?

4. A boat is pulled into a dock by a rope attached to the bow of the boat and passing through a pulley on the dock that is 1m higher than the bow of the boat. If the boat is pulled in at a rate of 0.8 m/s, how fast does the boat approach the dock when it is 10m from the dock?

So this would make a right-angle triangle, one side is 1m, the other 10m. I assume this would have something to do with Pythagorean theorem, but not sure how to apply it.

Thank you very much.