The first:

When the sum of 396 and four times a positive number is subtracted from the square of the number, the result is 84. Find the number.

What I did:

sqrt(x)-(396+4x)=84

sqrt(x)-396-4x=84

sqrt(x)-4x-312=0

-4x^2-x-97344=0

From here I am stuck, when I put it into the quadratic formula it gives me a negative and we aren't allowed to use imaginary numbers. I'm lost.

Here is the next problem:

A man built a walk of uniform width around a rectangular pool. If the area of the walk is square feet and the dimensions of the pool are feet by feet, how wide is the walk?

a=lw

l=w+4

207=w(w+4)

207=w^2+4w

0=w^2+4w-207

another negative in the quadratic equation...

Any help would be greatly appreciated!