(x+3)(x^2 + 5x +1) is the questions
= x^3 +5x^2+x+3x^2+15x+3.
We get this by using the distributive property.
= x^3+8x^2+16x+3
Simplify
So the answer is x^3+8x^2+16x+3
Hope this helps. If you have any questions, please put them in the comments below.