Final answer:
The equation for f(x + 3) is f(x + 3) = -x + 3.
Step-by-step explanation:
To write an equation for f(x + 3), we substitute x + 3 into the original equation f(x) = -x + 6:
f(x + 3) = -(x + 3) + 6
Simplifying, we get:
f(x + 3) = -x - 3 + 6
f(x + 3) = -x + 3
Therefore, the equation for f(x + 3) is: f(x + 3) = -x + 3.