To shift the function \( f(x) = (x + 1)^3 \) to the left by 3 units, you need to replace \( x \) with \( x + 3 \) in the function.
So the new function becomes:
\[ f(x) = (x + 3 + 1)^3 \]
This simplifies to:
\[ f(x) = (x + 4)^3 \]
Therefore, the equation describing the function shifted to the left by 3 units is:
\[ f(x) = (x + 4)^3 \]
So, filling in the blanks:
\[ f(x) = (x + 4)^3 + 0 \]