Physics question (answer provided)

Two identically charged objects are 6.2 nm apart.  If the electrostatic force between them is 53.9 pN, what is the charge on the objects?  Ans. 4.8 x 10-19 C

How do I get that answer?

Let Q1 and Q2 be the charge on each object, the
the force between two objects is defined by:

F = (k * Q1 * Q2) / ( r^2)

since the two objects have the same charge, Q, then

F = ( k * (Q^2) ) / ( r^2)

Where,

F = 53.9 * 10^-12 N

r = 6.2 * 10^-9 m

k = 8.99 * 10^9 (N m^2)/(C^2)

then,

Q =

square root of (

(53.9*10^-12) * (6.2*10^-9) * (6.2*10^-9)
over,
( 8.99*10^9)

) = 4.8*10^-19