<p>A capacitor in series with a resistance of 30<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>&#937;</mi></math>&nbsp;is connected to a.c. mains. The reactance of the capacitor is 40<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>&#937;</mi></math>. Calculate the phase difference between the current and the supply voltage.</p>