Complex numbers

( x - 1 )⁴ =16

( x - 1 )²= ±4

x-1 =   (±4)

so x-1 =  ±2 (taking +ve sign)  ==> x=3 or -1

and x-1 = ±2j where j=-1 (taking -ve sign)

so x = 1±2j

so sum of nonreal values of x = (1+2j)+(1-2j) = 2