The black disk is the occulting disk blocking out the disk of the Sun and the inner corona. The tick marks along the bottom of the image mark off units of the Sun's diameter. Select a feature that you can see in all five images, for instance the outermost extent of the bright structure or the inner edge of the dark loop shape. Measure its position in each image. Using the position and time, you can calculate the average velocity.
Velocity is defined as the rate of change of position.
Further Questions and Activities Select another feature, trace it, and calculate the velocity and acceleration. Scientists often look at a number of points in different parts of the CME to get an overall idea of what is happening. Sometimes it can be tough to trace a particular feature. You can measure their velocities and accelerations too.