haven't done this since college so rougly 8 years but let me give it a shot:
2x^2 * x + 3x * x + 5 * x = 2x^3 + 3x^2 + 5x
3x^2 * x + x * x + 3 * x = 3x^3 + x^2 + 3x
The coefficient of x is the sum of the coefficients of these terms, which is 5 + 3 = 8, and 3 = 11, respectively.
Adding them...