If f(z)=7−z1−z2 ,where z=1+2i ,then |f(z)|  is equal to

Given f(z)=7−z1−z2 Where z=1+2i ⇒|z|=1+4=5       (∵ z=a+ib  then |z|=a2+b2) ∴f(z)=7−z1−z2=7−1−2i1−(1+2i)2                                 =6−2i1−(1−4+4i)                                  =6−2i4−4i=3−i2−2i ⇒|f(z)|=|3−i2−2i|=|3−i||2−2i|                                     =9+14+4=52=|z|2