To find the decreased percentage,here's what we can do:

In this case,the eqaution would be:

Hope it helps!
I say A. because all the sides are the same.
HI
the answer is 200 millimeters
<333
18 - 7x = -20.5
Subtract 18 from each side:
-7x = -38.5
Divide both sides by -7:
x = -38.5 / -7
x = -5.5 = 5 1/2
The answer is D.