You may have divided 20 by the 2 to simplify. However, 2 is not a factor, because i is being subtracted from it. Treat the division as a fraction and rationalize the denominator.

$\displaystyle\frac{{20}}{{{2}-{i}}}=\frac{{20}}{{{2}-{i}}}\cdot\frac{{{2}+{i}}}{{{2}+{i}}}\usepackage{cmbright}\Huge\$