Answer:
9 mm wide
Step-by-step explanation:
Perimeter = length x 2 + width x 2
34 mm = 16 mm + ?
34mm = 16 mm + 18 mm
18/2 = 9
9 mm wide
Essentially, the rule goes as so: odd + odd = even, even + even = even.
Although that may not be the answer you're looking for, it is a math rule that is never debunked and essentially the premises for why you get an even sum practically always depending on the numbers.
Hope this helps!