I had immediately found that one, but was stuck on the algebraic rearrangement of equations that used to be very handy. In Mathcad <= 15.0, one could right click on any variable in an equation, and a pop-up window would give you the option to "solve for variable" - meaning that it would, if possible, rearrange the entire equation in terms of that variable. It was one of the best features of Mathcad, allowing rapid algebraic manipulation, substitution (also less convenient in Prime), and overall power to derive. I finally did figure it out for prime. Here was my first win.
Thank you, though, for answering. I like this community.