1) 15a - (a + 3b) + (2a - b) = 15a - a - 3b + 2a - b = 15a - a + 2a - 3b - b = 16a - b.

2) -5x - (3x - (2x - 4)) = -5x - (3x - 2x + 4) = -5x - 3x + 2x - 4 = -6x - 4.