Question 1151080
You probably wanted  {{{ Z = (Z1*Z2)/(Z1+Z2) }}}  (use parenthesis)<br>

<pre>

Z = {{{ ((6+4j)(6-j)) / ((6+4j)+(6-j)) }}} 
= {{{ (40+18j) / (12+3j) }}}
Multiply numerator and denominator by 12-3j:
= {{{ ((40+18j)(12-3j)) / ((12+3j)(12-3j)) }}}
= {{{ (178+32j)/51 }}} exact answer
= {{{ 3.490 + 0.627j }}}  to three decimal places

Polar form: left as an exercise.