two spherical balls lie on the ground touching . if one of the balls has a radius of 5 cm , and the point of contact is 7 cm above the ground , what is the radius of the other ball ?
"similar triangle properties . . 2 / r + 5 = 5 / r - 5 giving r = 35 / 3 . answer : c"
add(add(5, 7), 5)