How is gravity affected by mass and radius?

Gravity is directly proportional to the difference in mass ( thus, the greater the difference in mass of two objects, the greater the gravity).

Gravity is inversely proportional to the square of radius between two objects ( thus, the greater the distance from radius, thus, the lesser the gravity)

* Well if you mean the radius of an object, then it is directly proportional; greater the radius, greater the gravity.* 

Bis the correct answer.