Creating A Numerical Integration Function

I'm a VERY basic user of Excel. I have a mathematics and programming background, but no knowledge or experience in VBA programming.

I'm wishing to create a new function as a VBA custom function procedure to numerically intergate an expression (such as 3*X^3 + 2*X^2), defined by a worksheet formula (not by data points). The five parameters required by the function would be in the form of cell references which point to (1) the expression to be integrated (such as the above example), (2) the integrating variable (in this example, X), (3) the lower limit of X, (4) the upper limit of X, and (5) a tolerance value for termination.

I've been trying to implement the Trapezoidal Method - but not a flicker of light so far!!.

I understand the Formula property of a cell may be used to get the expression to be integrated into the VBA code as text. Then the Substitute function may be used to replace the variable of interest by a value, and the Evaluate method may be used to get the new value of the expression. I have no experience in implementing these steps.

I've made extensive attempts to do the above, but without success so far. ("I started off with nothing, and still have most of it left"!).

I'm hoping someone may be able to assist me, or else point me to a relevant area of the forum (or elsewhere), by demonstrating the methods and techniques needed to achieve the function I'm seeking. Perhaps it has all been done before, but I haven't located it.