"Suppose some sort of clamp is applied to hold an electron fixed at the distance of 2.5 Angstroms from a lithium nucleus Li3+ which is also clamped into position. Calculate the magnitude of the force between the two fixed particles."

The books says the answer is:
-2.304 x 10^-9 N

I've tried the problem several times and keep getting:
-1.107x10^-8 N

I've been using the equation
F(r) = [(q1)(q2)/[(4)(PI)(Epsilon naught)(r^2)]

Could someone please help me out? Thank you.