A box contains 7 red marbles, 5 white marbles, and 3 blue marbles. If a marble is randomly selected from the box, what is the probability that it is white? Express your answer as a fraction or a decimal number rounded to three decimal places, if necessary.

The party planning committee has to determine the number of tables needed for an upcoming event. if a square table can fit 8 people and a round table can fit 6 people, the equation 150 = 8x + 6y represents the number of each type of table needed for 150 people.