When using the formula for impedance you have to substitute the impedances with their directions. That is why we normally use the complex number method in evaluating AC circuits. You have only substituted the magnitude of impedances which is incorrect. I suggest you to read http://www.phy.duke.edu/~fortney/phy...rcuit_note.pdf which will give you a better idea.
In solving this problem the easiest method is to draw the two phasors in a vector diagram and find the resultant vector.