What is the ratio of the base-radius and slant height of a cone made by rolling up a semicircle?

What is the area of the curved surface $\left({\mathrm{cm}}^2\right)$ of a cone of base radius $12$ centimetres and slant height $25$ centimetres?

What is the surface area of a cone of base diameter $30$ centimetres and height $40$ centimetres?
(Note: Consider $\mathrm{\pi }=\frac{22}{7}$)