Question 139715
The radius of the original circle needs to be the slant height of the cone.  The slant height is the length of any line segment that connects the apex of the cone with any point on the perimeter of the base.  The slant height is also the hypotenuse of a right triangle where one of the sides is the height of the cone and the other is a radius of the base.


So, you are given the circumference of the base, 60 cm, which we know to be equal to {{{2*pi*r}}}.  That means that the radius is {{{r=60/(2*pi)=30/pi}}}


You are given the height, 25cm, so the slant height, s must be {{{s=sqrt((30/pi)^2+25^2)}}}. 


Ewwww! THAT looks ugly.  Looks like you have some calculator work to do.