Hello, Yuliya,
Let's set the length of a square's side to x. If the side lengths, x, of a square are tripled:
a. The length multioplier is 3 [3x for each side]. Percentage increase is 200% [((final-initial)/initial)*100%)] ((3x-1x)/1x)*100 = (2x/1x)*100 = 200%
b. Percentage decrease to return to original is %Decrease = -100(Final-Initial)/Initial [%Decrease = -100(1x-3x/3x), -100(-2x/3x), = 66.667% [I'm not sure what the "associated multiplier" is for this. Perhaps -92/3)??]
c. Perimeter is 4*x for the original. For the larger square it would be 4(3x) or 12 x. The original area is x2. The tripled length area would be (3x)2 or 9x2.

Robert S.
10/16/21
Yuliya D.
Thank you10/16/21