Quadratics with equal roots.

I think this is the right place to post this, I'm in England and don't know how the American schooling system works, but here goes:

"Find the values of k for which kx(sq)+8x+k = o has equal roots."

I know that for this equation to have equal roots the discriminant must equal zero, so:

b(sq)-4ac = 0

Putting numbers into this I get:

64-4k(sq) = 0

64=4k(sq)

This is where i get stuck - do I first square root each side, giving:

8=4k

and getting an answer 2, or do I first divide each side by 4, giving:

16=k(sq)

and getting 4 as the answer?

So to sum up, do I square root first, or simplify first?

Thanks in advance.