If a + b = -6a+b=−6a, plus, b, equals, minus, 6 and x + y + z = 3x+y+z=3x, plus, y, plus, z, equals, 3,
what is -3z - 3y - a - b - 3x−3z−3y−a−b−3xminus, 3, z, minus, 3, y, minus, a, minus, b, minus, 3, x?

The distribution of the amount of money spent by students for textbooks in a semester is approximately normal in shape with a mean of $235 and a standard deviation of $20. according to the standard deviation rule, how much did almost all (99.7%) of the students spend on textbooks in a semester?