Solve equations in Wolfram with given variables

Question

I am trying to use an equation as a template in Wolfram Alpha where the variables change. The equation is $-n = m - x\left\lbrack a - w\left(x - \frac{2l}{3}\right)\right\rbrack - w\left(x - \frac{2l}{3}\right)\left(\frac{l}{3} + \frac{x}{2}\right)$ and I want to solve for when $x = \ldots y = \ldots l = 1\ldots$ etc Can someone tell me what format I need to use. I can solve it for one variable ( if I type in where $x = \ldots$ at the end it substitutes it in but I can't put in any others ).

Answer 1

 evaluate  -n=m-x[a-w(x-(2 l)/3)]-w(x-(2 l)/3)(l/3+x/2) at x = 1, y = 1, l = 1

See this WA session

However, why not use somethong like SAGE, Maxima, Mathics, GAP or another Computer Algebra System?

Some even have an online version that lets you program and write and manipulate functions more naturally, but you can download as many on the web site are open source (free).