How to get return value from a method called dynamically?

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C#

For example I have the following code (input by user):
10*2
I have to include it in my dynamic source code like as:

//using ...
"public float Calc() {
return " + myTextBox.Text + "; }"

Now after building the dynamic assembly, I can invoke it using Type.InvokeMember, but I want to get the result returned by the method invoked (as with the above input, I want to get the value 20), could you please tell me how to achieve that? Do we have to invoke the method without using Type.InvokeMethod?
Your help would be appreciated!
Thanks!