What is the sum of two solutions of the quadratic equation ax^2+bx+c=0

Monitors manufactured by tsi electronics have life spans that have a normal distribution with a standard deviation of 1800 hours and a mean life span of 20,000 hours. if a monitor is selected at random, find the probability that the life span of the monitor will be more than 17,659 hours. round your answer to four decimal places.

Sole the equation 6n + 9 = -3n - 21 - 6 for n

Which is the graph of the linear equation x – 2y = 6?