Help understanding a physics question?

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I am trying to understand how to solve an equation. I have the answer to the problem and an example, but I am just not understanding the process. Can someone please try to explain it to me in simple terms? In the example I also do not understand where the (9.0 x 109 N•m2/C2) comes from. Thank you so much in advance.

Question:
Determine the electrical force of attraction between two balloons with separate charges of +3.5 x 10^-8 C and -2.9 x 10^-8 C when separated a distance of 0.65 m.

Answer: 2.16 x 10^-5 N, attractive

Step 1: Identify known values in variable form.

Q1 = +3.5 x 10^-8 C and Q2 = -2.9 x 10^-8 C
d = 0.65 m

Step 2: Identify the requested value

F = ???
Step 3: Substitute and solve

(See example B on the Tutorial page for sample algebra.)

Example B
Two balloons are charged with an identical quantity and type of charge: -6.25 nC. They are held apart at a separation distance of 61.7 cm. Determine the magnitude of the electrical force of repulsion between them.
Given:
Q1 = -6.25 nC = -6.25 x 10^-9 C
Q2 = -6.25 nC = -6.25 x 10^-9 C
d = 61.7 cm = 0.617 m
Find:
F elect = ???

Solve:
F elect = k • Q1 • Q2 / d2
F elect = (9.0 x 109 N•m2/C2) • (6.25 x 10^-9 C) • (6.25 x 10^-9 C) / (0.617 m)^2

F elect = 9.23 x 10^-7 N