Question

Now that you know the height of the cone how can you solve for the slant height?

Answer 1

imagine a triangle

one side is just upwards trough the cone, one side is the radius of the circle and the last one is the slant height.

remember the pythagoras stuff

so

(slantheight)² = radius² + height²

or finally:

slantheight = squareroot (radius² + height²)