Write the variation and find the quantity indicated. F varies jointly as q1 and q2 and inversely as the square of d. If F=12 when q1 =3, q2=9 and 9=3

Question

The variation of F=

Answer 1

set F = k (q1 q2/d^2)

plug in the values, (I think you have a typo and you meant to say .... d = 3

12 = k(3)(9)/(9)
k = 4

so F = 4q1 q2/d^2