To find the Xc that makes the voltage in phase with the current, you have to find the equivalent impedance of that branch. Then, you can find the current through Ohm's first law. So you have to think a little with these results. If you use phasor diagram may help you to understand this phenom.
Well, the input impedance is given by:
Let's say that the input voltage is a sine wave without any phase difference, so we need that: