Tangent line and velocity problems

I'm having some trouble with some of these. It's kinda one of those times where you're doing great in class and then you leave and can't remember anything (Headbang)

1. If a rock is thrown in the air on a small planet with velocity 25 m/s, its height in meters is Y = 25t - 4.9t^2. What is the rock's velocity at t = 3?

2. The slope of the tangent line to the curve Y = 4(sqrt[x]) is _______. The equation for the line is Y = mx + b, where M is ______ and B is ______.