So, I'm studying for an upcoming Calculus test, and I am stuck on only three problems.

1. Find the absolute or local maximum and minimum of f(x)=8-2x if x is greater than or equal to 6

- I pretty much just plugged 6 in for x and then 0 and.. yeah. I'm not really sure. I got -4 is an absolute minimum, but I doubt that's correct.

2. Find the critical numbers of f(x)=x^4(x-3)^3

- For this one, I found the derivative and was going to set it to 0, but I get a little confused. I end up with [4x^3(x-3)^3]+[3x^4(x-3)^2], and I don't know how to set that equal to 0 or if it can be simplified further.

3. Find the maximum or minimum of F(x)=(1-x^2)+6x^2

- Again, I found the first derivative and still got confused finding it (to set it to 0). I understand derivatives; it's just setting them equal to 0 that confuses me.

Any help will be greatly appreciated.