Using an equation like d = rt, create cards for each item, variable, equal sign and operators. On the back of the operator card, put the inverse operation (hopefully you will have had that lesson with your students already)
Choose a variable to solve for. I chose to solve for r. Remember, the back of the operator has it's inverse operation, so you would have this:
So I thought, maybe this is too easy. So I tried it with converting Celcius to Farenheit.
For fractions, use reciprocals on the back: