Answer:

m= 16.8

Step-by-step explanation:

So your equation is just like this m=kn/r

So now lets find the constant k

m=kn/r

9=k5/4

k = 36/5

Now, the value of k = 36/5

Next find "m"

m=kn/r

m=(36/5)(21)/9

m= 16.8

So the value of m is equal to 16.8