How do you find the independent variable with this information?

Use the normal approximation to the binomial distribution to answer this question. fifteen percent of all students at a large university are absent on mondays. if a random sample of 12 names is called on a monday, what is the probability that four students are absent?

What is the perimeter of an equilateral triangle if each side is (x+3)?

What is the interquartile range of this day at set?