where C(n,k) is the binomial coefficient, which is equal to n! / (k!(n-k)!).
In this case, a = 3x and b = -1/2x^2, and n = 6. We can plug these values into the formula and find the term that does not contain any x variables.
The term independent of x will be the term where the exponent of x is 0. This occurs when k = n in the binomial coefficient formula. So, the term independent of x is: