To calculate the resultant velocity of two velocities in opposite directions, you need to subtract the velocity in the opposite direction from the velocity in the other direction. The resultant velocity will have a magnitude equal to the difference between the magnitudes of the two velocities and will be in the direction of the velocity with the larger magnitude.

For example, if you have two velocities of 10 m/s to the right and 5 m/s to the left, the resultant velocity would be 10 m/s - 5 m/s = 5 m/s to the right.

Here are the steps to calculate the resultant velocity of two velocities in opposite directions:

1. Draw a vector diagram of the two velocities.

2. Label the vectors with their magnitudes and directions.

3. Find the difference between the magnitudes of the two velocities.

4. The resultant velocity will have a magnitude equal to the difference between the magnitudes of the two velocities.

5. The resultant velocity will be in the direction of the velocity with the larger magnitude.

Here is an example of how to calculate the resultant velocity of two velocities in opposite directions:

```

10 m/s -->

|

|

5 m/s <--

```

In this example, the two velocities are 10 m/s to the right and 5 m/s to the left. The resultant velocity will have a magnitude of 10 m/s - 5 m/s = 5 m/s to the right.

Here is the vector diagram for this example:

```

10 m/s -->

|

|

5 m/s <--

```

The resultant velocity is 5 m/s to the right.