**Given Information:**

- A charge of +12μC is located at x = 20cm on the x-axis.
- A charge of -18μC is located at x = 29cm on the x-axis.
- The charge we need to find the force on is +18μC.

**Calculating the Distance:**

To calculate the distance between the charges, we need to find the difference between their positions on the x-axis.

Distance = Final Position - Initial Position
Distance = 29cm - 20cm
Distance = 9cm

**Calculating the Force:**

To calculate the force between the charges, we can use Coulomb's Law equation:

Force = (k * q1 * q2) / r^2

where k is the electrostatic constant (8.99 x 10^9 N m^2/C^2), q1 and q2 are the magnitudes of the charges, and r is the distance between the charges.

Plugging in the given values:

Force = (8.99 x 10^9 N m^2/C^2) * (12 x 10^-6 C) * (18 x 10^-6 C) / (9 x 10^-2 m)^2
Force = (8.99 x 10^9) * (12 x 18) / 81
Force = 2 x 10^10 N

**Determining the Direction:**

The direction of the force depends on the sign of the charges. Like charges (positive with positive or negative with negative) repel each other, while opposite charges (positive with negative) attract each other.

In this case, the +18μC charge is positive and the -18μC charge is negative. Therefore, the force on the +18μC charge will be directed away from the -18μC charge, i.e., in the positive x-axis direction.

**Conclusion:**

The magnitude of the force on the +18μC charge is 2 x 10^10 N, and the direction of the force is in the positive x-axis direction.