Answer:
(a)By keeping the distance square constant.
(b) By keeping both the masses constant.
Step-by-step explanation:
According to the gravitational force of attraction, the force will be,

(a) We can take the F is on the y axis and the MM on the x axis we can plot a straight line by keeping the
constant to prove attractive force is directly proportional to MM.
(b) We can take the F is on the y axis and the distance
on the x axis and we can plot a curve type graph by keeping the MM constant to prove attractive force inversely proportional to distance square.