we know that
the dimensions of the original rectangle are
18.6 mm x 31 mm
the dimensions of the reduced rectangle are
3 mm x ? mm
step 1
find the scale factor
scale factor=3/18.6------> 1/6.2
then
the other dimension of the reduced rectangle is
31*(1/6.2)-----> 5 mm
perimeter of the reduced rectangle=2*[3+5]-----> 16 mm
the answer is
The perimeter of the reduced rectangle is 16 mm