For charge q3 to maintain equilibrium, the total force acting on it must equal zero.
Suppose we denote the total distance traveled by the car as L (this is for ease of understanding).
We can formulate a system of equations to derive a solution. Let’s assume the distance from q1 to q3 is r_1 and the distance from q3 to q2 is r_2, which must satisfy the equation:

The second equation will represent the total force on charge q3:

k_c symbolizes Coulomb's constant. Given that the left side equals zero, we can divide the entire equation by k_c to eliminate it:

Next, we will solve this for r_1^2:

Now, we have a quadratic equation with the following parameters:

The two solutions can be expressed as:

We require a positive solution. When we input all values, we derive: