So this is the question (it's a volume question, and I'm pretty sure I can figure out the second part of finding the volume but finding the slant height seems very difficult here!) And it would also be very very helpful if you guys can point out as to how to get the answer.

Q: The ratio of the slant height and perpendicular height of a cone is 5:4. The diameter of the base is 12cm. Find the slant height of the cone.

All help greatly appreciated