WeBWorK doesn't have an built-in integrated solver. It is not a CAS such as maple or Mathematica and in general can't solve problems like this symbolically.

Since we are talking about homework problems the first question to ask is how should the student solve the problem? Is this a question designed to encourage use of Newton's method or something like that? If so then it is easy to program Newton's method into the problem (there is also PGnumericalmacros.pl package that has some numerical integration routines)

Another technique is to choose the answer at random and then create the question (for example this will allow you to guarantee that the roots of polynomials come out to even integers). An intermediate version is to create an equation at random -- apply Newton's method to attempt to find the zero -- if the Newton's method doesn't converge, change the equation and try again. Once you have a suitable question which can be solved easily/quickly by Newton's method present the question to the student.