Question

Figure (a) shows charged particles 1 and 2 that are fixed in place on an x axis. Particle 1 has a charge with a magnitude of |q1| = 12.0e. Particle 3 of charge q3 = +13.0e is initially on the x axis near particle 2. Then particle 3 is gradually moved in the positive direction of the x axis. As a result, the magnitude of the net electrostatic force on particle 2 due to particles 1 and 3 changes.

Figure (b) gives the x component of that net force as a function of the position x of particle 3. The scale of the x axis is set by xs = 1.70 m. The plot has an asymptote of F2,net = 1.370 × 10-25 N as x → ∞.

As a multiple of e and including the sign, what is the charge q2 of particle 2?

Here are the two figures:
h t t p : / / i . i m g u r . c o m / I U C 3 6 . p n g