First, let's simplify the expression inside the parentheses step by step:

Step 1: 5 * (-0.8) = -4
Step 2: -12 + (-4) = -16

Now we have: (-16) * (30 / 6, 45) - 1074

Simplify the expression inside the parentheses further:

Step 3: 30 / 6 = 5
Step 4: 125 - 80 = 45

Now we have: (-16) * (5, 45) - 1074

Simplify the expression inside the parentheses again:

Step 5: 5 * 45 = 225

Now we have: (-16) * 225 - 1074

Step 6: -16 * 225 = -3600

Now we have: -3600 - 1074

Step 7: -3600 - 1074 = -4674

Therefore, the final answer is -4674.