Task: Question Answering
Input (English): Problem: two spherical balls lie on the ground touching . if one of the balls has a radius of 9 cm , and the point of contact is 10 cm above the ground , what is the radius of the other ball ( in centimeters ) ? 
Options: a ) 50 / 4 , b ) 70 / 6 , c ) 80 / 7 , d ) 90 / 8 , e ) 100 / 9
Output (English): d