This is a mathematical expresion, not a question.

If you copy the question from a book, most probably the instructions are at the beginning of a number of questions. It could be "simplify the following expressions:", or "factorize", etc.

I assume it is "simplify".

x + 3x^2 + x^2

collect like terms:

3x^2+x^2 + x

= 4x^2 + x