Find the number of units x that produces a maximum revenue R

1. R= ((1,000,000x))/((.02x^2+1800))

Now I think I am supposed to differentiate this then set it to zero to find the number but what would I use quotient rule?

Find the number of units x that produces the minimum average cost per unit c

C=3000x-x^2 square root(300-x)

Since cost is C/x

I did

((3000x-x^2 square root(300-x))/((x))

I am stuck here the radical is kind of confusing me if I took out the x would I just be left with

x-square root 300 ? and then I have to take the derivative of that and set it to zero?