Answer:
x = 3 and x = -12
Explanation:
To solve an absolute value equation, you create two equations, one where the right side is negated and one where the right side isn't:
| 2x + 9 | = 15 becomes:
2x + 9 = 15 and 2x + 9 = -15
2x = 6 and 2x = -24
x = 3 and x = -12
Why this works is that |-x| and |x| will both be equal to 0. Remember that absolute value is the distance a number is away from 0.