The correct answer is: -18 .
________________________________________
9i * 2i = 18 i² .
________________________________________
" i " is an imaginary number equal to "√(-1) " .
" i² " = [√(-1)] ² = √(-1) * √(-1) = -1 .
________________________________________
18 * i² = 18 * -1 = -18 .
________________________________________