Jeez I don't understand how you guys answer this so fast and accurately, but here is another.

sqrt (4225)  =   65  = side of the square

So....the perimeter of the park  =  4 * 65  =  260 ft

So......the length of wire needed  is

First perimeter + Second perimeter + Third perimeter + Fourth perimeter  = 

260 + 260(1.05) + 260(1.05)^2  + 260(1.05)^3  ≈  1120.6 ft

length of one side of park   =   √[ 4225 sq m ]  =   65 m

perimeter of park   =   4 * 65 m   =   260 m

length of each circuit  =   5% greater than 260 m   =   105% * 260 m   =   273 m

total length needed  =  4 * 273 m   =   1092 m

I think they have used 5% simple (non-compound) increase:

[260 x 4] + [5% x 260 x 4] = 1040 + 52 =1092 m.