What is the reason for the second statement in the proof

When using the linear combination metho e linear combination method to solve a system of linear equations, the four options are:

Assume that the weights of quarters are normally distributed with a mean of 5.67 g and a standard deviation 0.070 g. a vending machine will only accept coins weighing between 5.48 g and 5.82 g. what percentage of legal quarters will be rejected? round your answer to two decimal places.

Solve each quadratic equation by factoring and using the zero product property. x^2 + 18x = 9x