The symbolics does not know anything about units. So it does not know that lbf = lb*s^-2*ft and therefore it can't simplify its results.
I see no reason for using the symbolics as you are only after numeric results.
You already have provided guesses for the three variables, so stay with numeric solutions.
Because your three variables aren't of the same dimension (different units), Mathcad can't display them in one matrix, but you always can assign the result to a vector with separate variables and display them singly:

Mathcad would display the results using just the base units of the chosen unit system and lbf is a derived unit. So just type lbf in the unit placeholder after the displayed result and Mathcad will care for the rest.