5,2.5,7.5 is it a right triangle

Use the elimination method to find the solution to the system of equations. 2x - 3y = -9 -x + 3y = 6

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?

Need on this geometry question. explain how you did it.