Answer: To solve the equation -2a - 9 = 6a + 15 and find the value of a, we can follow these steps:
Step 1: Combine like terms
-2a - 9 = 6a + 15
To combine like terms, we need to move the variables (a) to one side of the equation and the constants (numbers without variables) to the other side. We can do this by adding 2a to both sides of the equation and subtracting 15 from both sides:
-2a - 9 + 2a - 15 = 6a + 15 + 2a - 15
Simplifying, we get:
-9 - 15 = 6a + 2a
Step 2: Simplify both sides
-24 = 8a
Step 3: Solve for a
To isolate a, we can divide both sides of the equation by 8:
-24/8 = 8a/8
Simplifying, we get:
-3 = a
Therefore, the value of a that satisfies the equation -2a - 9 = 6a + 15 is a = -3.