How can I copy equations?

Here is my current case, I have a global variable for bend allowance: my formula looks like this:

BA=PI * "A@sketch1"/180*("R@sheet-metal" + ("Thickness" * "K@sheet-metal"))

Now I want to copy that and edit to this:

BA90=PI * .5*("R@sheet-metal"  + ("Thickness" * "K@sheet-metal"))

The specifics are not important. I just wanted to ask the question in context.

How can I make a copy of an existing equation?