My students have such a problem with literal equations, especially when they have to rewrite them. It might be because I do not give them enough practice in rewriting the equations themselves.
I am guilty of teaching formulas and literal equations in only one way and I don't teach them to find different things. In Geometry, I had them find the area only. I did not ask them to find the base given the area.
CPalms has a nice lesson plans with everything needed to introduce the topic. I like the way it includes the necessary materials to accompany the lesson.
One way I've taught this type of thing is with sticky notes on the board that I could physically move around. I write the variable on the sticky note, put it on the board as an equation, then move it around step by step. I've passed out a ton of sticky notes to the kids to use on their white boards to go through the same process.
Hands on High School Math recommends using cards such as 3 x 5 cards cut in half with variables and operations written on them. So you could create R x T = D using one card for each term. Then they can rearrange the cards to form the new equations such as D/R = T. I like the idea of using cards better because I can laminate them for future use. This is much better than using sticky notes.
The Math = Love site suggests a scavenger hunt as a way to practice rewriting literal equations. I enjoy the way she has it set up although I've been known to set one up using QR codes. The only thing I missed in the examples was the statement on rewriting it to find x or y. This is important. I think I'll do one with the standard equations such as I = PRT or A=LxW.
I would add one thing to this and that is give students some numbers to use in the various equations to get answers. My students are not good at going from the literal formulas to substituting values in for real answers. I'm hoping by adding this in, my students might be able to transfer their knowledge.
Better Lesson has a nice fully developed lesson from a brainstorming introduction, to a guided notes and practice, a partner activity and a closing activity that includes an exit ticket. I like that this has the power point presentation for the guided notes, the worksheets for the practice activity and a do now or warm-up at the beginning. I like the way the lesson is fully developed and ready to go. I plan to try this.
These resources when integrated will provide a nice unit for literal equations. I will be teaching it in about two weeks.