Answer: f(x+3) = -5x -9
Step-by-step explanation: Start by substituting (x+3) for x. When you do this, you'll get the answer
f(x + 3) = -5 (x + 3) + 6
When you multiply out the (x + 3) by the -5, you'll get an answer of (-5x -15), which gives you the full equation
f(x + 3) = -5x -15 +6
Now, you just have to combine the like terms of -15 and +6, or, 6-15, to get -9.