beginner solver question

hello all,
i presently have a vba macro that takes the number in cell A1 as an argument and outputs a number to cell A2. I would like to figure out what value of the argument (A1) will produce an output (A2) equal to a specified number, x say.

So I was hoping to get the Solver to optimize A1 until A2=x as follows:
1. guess A1
2. run macro
3 compare A2 to x
4. repeat until A2=x

However, I did not see an option in Solver that will allow me to do step 2. Can you please advise.

Thanks!

Solver. the macro is a black box.
But now that you mention it, it just occured to me that I could just write my own macro to optimize.

In any case, it doesn't look like Solver has the capability to update the target cell by running a macro.