Notice that the "a" in the function definition and the "a" in the function call look different? That's because the label for one is set to "variable". but for the other it's set to "function". They need to be set the same. Also, the symbolic processor does not really understand units. Notice that the "m" and "s" from the symbolic evaluation display as variables, not units. Split the symbolic evaluation from the function definition. When you call the function you also have "s" as a variable, which is not defined, rather than the defined unit for seconds. If you fix the other problems Mathcad should fix that for you automatically though.
