3.

(a). The cost($C) of making a cylindrical rod varies jointly as the square of it's base radius(r cm) and it's height(h cm). It cost $50 to make a cylindrical rod of base radius 2 cm and a height of 5 cm.

(i). what is an equation involving Cost, radius and height of the cylindrical rod and use it to find the constant of variation.

(ii). What will be the radius of the cylindrical rod if the height of 6 cm cost $240 ?