When you FOIL it out, you get
9u² + 48uv + 64v² .
and that's IT.
There's only one way to simplify that expression.
Let's be honest with each other. If we were given
9u² + 48uv + 64v²
and asked to simplify it, we would write it as (3u + 8v)²
just as fast as we could !