Find the total surface area of a cone, if its slant height is 21 m and diameter of its base is 24 m.

It is given that:

Diameter of the cone (d) = 24 m

Radius of the cone(r) = 24/2 = 12 m

Slant height of the cone (l) = 21 m

T. S. A = Curved Surface Area of Cone + Area of Circular Base

$=\pi * r * l+\pi * r^{2}$

$=(22 / 7 * 12 * 21)+(22 / 7 * 12 * 12)=22 / 7 * 12(12+21)=1244.57 \mathrm{~m}^{2}$

Therefore the total surface area of the cone is $1244.57 \mathrm{~m}^{2}$.