To find \((f \circ g)(x)\), we need to substitute \(g(x)\) into \(f(x)\).
### Given functions:
- \( f(x) = x^3 + 8x + 15 \)
- \( g(x) = x + 5 \)
### Finding \( (f \circ g)(x) \):
1. Compute \( g(x) \):
\[
g(x) = x + 5
\]
2. Substitute \( g(x) \) into \( f(x) \):
\[
f(g(x)) = f(x + 5)
\]
3. Now, replace \( x \) in \( f(x) \) with \( x + 5 \):
\[
f(x + 5) = (x + 5)^3 + 8(x + 5) + 15
\]
4. Calculate \( (x + 5)^3 \):