Please don't take this down, I genuinely do not understand it!

Let X and Y be the following sets:

X = {5,10,15}
Y = {3,6,9,12,15}

Which of the following is the set X∪Y ?
CHOOSE ONE ANSWER
A. {3,6,9,12,15}
B. {5,10,15}
C. {3,5,6,9,10,12,15}
D. {}

Which approach to the theory-and-research cycle does the following sequence reflect: (1) specific observations suggest generalizations, (2) generalizations produce a tentative theory, (3) the theory is tested through the formation of hypotheses, and (4) hypotheses may provide suggestions for additional observations?

What is the value of x in the following equation? -3x-2=2x+8

State one method by which you can recognize a perfect square trinomial.