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

Given :
Radius (r) of the base of cone = \(\frac{24}{2} cm = 12 cm\)
Slant height (l) of cone = 21 cm

We know that, TSA of cone
= \({\pi}r(r + l)\)
= [\(\frac{22}{7} × 12 × (12 + 21)\) \({m}^2\)]
= [\(22 × 1.71 × 33\) \({m}^2\)
= 1244.57 \({m}^2\)

Therefore, the total surface area of the cone is 1244.57 \({m}^2\).