Answer:
add 18 to both sides, giving you 3x = 96
You have 28 meters of fence to make 3 sides.
28/3 = 9.3333
The pen will be 9.3333 by 9.3333 meters
Diameter of the larger gear х см
1/4х = 16 - 2.5
1/4x = 13.5
x = 13.5 * 4
x = 54 cm - diameter of the larger gear /