The solution to 5b-13=22 is 7
After the 3rd pick we have: 4 white, 3 red and 8 black marbles.
The probability that the 4th marble is black is:
P ( Black ) = 8 / 15 = 0.5333
After the 4th pick we have: 4 white, 3 red and 7 black marbles.
P ( Red or Black ) = 10 / 14 = 5 / 7 = 0.7143
4x - 24 = -2x + 30
4x + 2x = 30 + 24
6x = 54
x = 9
answer: the number is 9