9a + -3(2a + -4) = 15 Reorder the terms: 9a + -3(-4 + 2a) = 15 9a + (-4 * -3 + 2a * -3) = 15 9a + (12 + -6a) = 15 Reorder the terms: 12 + 9a + -6a = 15 Combine like terms: 9a + -6a = 3a 12 + 3a = 15 Solving 12 + 3a = 15 Solving for variable 'a'. Move all terms containing a to the left, all other terms to the right. Add '-12' to each side of the equation. 12 + -12 + 3a = 15 + -12 Combine like terms: 12 + -12 = 0 0 + 3a = 15 + -12 3a = 15 + -12 Combine like terms: 15 + -12 = 3 3a = 3 Divide each side by '3'. a = 1 Simplifying a = 1