I'm not sure if this dividing,multiplying,subtracting or adding but for adding i got 6 as my answer.I don't know if this the correct answer but its better than having no answer right?
What about it that is not a question
Answer:

Step-by-step explanation:
Given


Required
How fast is the ball seem to be moving?
This question illustrates relative velocity;
Since the ball and the train moves in the same direction, the required velocity relative to the person standing behind is:

i.e. we add both velocities


If the intersection of two sets is a null set or an empty set, then two sets A and B are disjoint sets. The intersection of a set is therefore empty.
<h3>Explain about the disjoined set?</h3>
Disjoint sets are a pair of sets that do not share any elements. For instance, the sets A=2,3 and B=4,5 are not connected sets. However, set C=3,4,5 and set C=3,6,7 are not disjoint since 3 is a common element in both sets C and D.
Now that we are clear on the disjoint set's definition, let's go on to talking about some more important topics, such the notation and Venn diagram related to it. A B = is the notation used for this particular set. As an illustration, suppose A = 1, 2, 3, and B = 4, 5, 6, 7. A + B = then.
To learn more about disjoined set refer to:
brainly.com/question/28165517
#SPJ1