Can you specify what error you are encountering?
You can use Mendix functions to multiply numbers, not textual input, so make sure that you define A and B as Integers in your domain model. Also see the Mendix documentation for more information about arithmetic functions.
A solution could be:
1. Set up your domain model in a correct fashion. The values should be Integers (numerical values).
2. Create a form that only shows Value A and Value B:
3. You need to create a Multiply entity first, so make a Microflow that a. does this, b. opens the form and passes the Multiply entity to the form that you just created:
4. On the page that you created, create a microflow that calculates the values of A and B and changes the value C of the Multiply object:
5. Finally, create a new form that shows the value of C and make sure that the input box has its Editability set to Never :
6. Lastly, connect your new read-only form to the calculating microflow, showing the result of the calculation in your read-only form!
What it looks like: