1. - 12d - d +5t^3 + 12t^3 + 9d 2. 13x - 5z - 12x - 8x + 12z 3.7n^2 - 14n^2 + 15n^2 +12u + 13 u

Let's simplify each expression step by step.

1. Expression: \(-12d - d + 5t^3 + 12t^3 + 9d\)

   Step 1: Combine the \(d\) terms: \[ -12d - d + 9d = (-12 - 1 + 9)d = -4d \]

   Step 2: Combine the \(t^3\) terms: \[ 5t^3 + 12t^3 = (5 + 12)t^3 = 17t^3 \]

   Final Result: \[ -4d + 17t^3 \]

2. Expression: \(13x - 5z - 12x - 8x + 12z\)

   Step 1: Combine the \(x\) terms: \[ 13x - 12x - 8x = (13 - 12 - 8)x = -7x \]

   Step 2: Combine the \(z\) terms: \[ -5z + 12z = (12 - 5)z = 7z \]

   Final Result: \[ -7x + 7z \]

3. Expression: \(7n^2 - 14n^2 + 15n^2 + 12u + 13u\)

   Step 1: Combine the \(n^2\) terms: \[ 7n^2 - 14n^2 + 15n^2 = (7 - 14 + 15)n^2 = 8n^2 \]

   Step 2: Combine the \(u\) terms: \[ 12u + 13u = (12 + 13)u = 25u \]

   Final Result: \[ 8n^2 + 25u \]

Summary of Results:

1. \(-4d + 17t^3\)
2. \(-7x + 7z\)
3. \(8n^2 + 25u\)