Lefty recognized the trick part right off - this is a problem in electronics, not mechatronics.
You're in the wrong classroom.
Also, your instructor tricked you - it's a really a trivial problem. As everyone here obviously
knows [except OP], you go to the basics for opAmp operation, and then solve for the special
case.
I really hope I can solve it ..
We all hope you can solve it too.