To find the resultant velocity when combining two velocities going in opposite directions, you need to subtract the velocities. The direction of the resultant velocity will be the same as the direction of the velocity with the greater magnitude.

For example, if you have two velocities, one with a magnitude of 10 m/s to the right and another with a magnitude of 5 m/s to the left, the resultant velocity would be 5 m/s to the right.

Here is the formula for finding the resultant velocity of two velocities going in opposite directions:

$$v_r = v_1 - v_2$$

where:

- \(v_r\) is the resultant velocity

- \(v_1\) is the velocity of the first object

- \(v_2\) is the velocity of the second object

If the two velocities are going in the same direction, the resultant velocity is simply the sum of the two velocities.