A bucket of height 16 cm made up of metal sheet is in the form of frustum of a right circular cone with radii of its lower and upper ends as 3 cm and 15 cm respectively. What is the slant height of the bucket?

20 cm

$r_1=3cm,r_2=15cm,h=16cm$

$l=\sqrt{(r_2-r_1)^2+h^2}=\sqrt{(15-3)^2+16^2}$

$=\sqrt{12^2+16^2}=4\sqrt{3^2+4^2}$

$=4×5=20cm$