The only difference between speed and velocity is that velocity also includes direction, so if the speed is the same but the velocity is changing, that means that the direction is changing on the ride, but the speed is staying the same.
Angles three and four are a linear pair, meaning that they they form a line. When two angles make a line, the measures add up to 180°. Adding the two values together, we see that 3x+27x=180. Simplifying and solving for x, we get 30x=180 ⇒ x=6.
The question, however, is asking for the measure of angle 4. Thus, we plug x=6 into 7x to get 6(7)=42.
Hope this helped!
Your answer would be 19/20 :)