Blue: P=4x +2+7x +7+5x-4 --> 16x +9-4=16x +5
Red: P=x+3+2x - 5 + x + 7 --> 4x + 10 - 5 = 4x + 5
Difference between the perimeter:
(16x + 5) - (4x + 5) = 16x + 5 - 4x - 5 = 12x
Perimeter when x = 3
Blue : 16x + 5 ⇒ 16(3) + 5 = 48 + 5 = 53
Red: 4x + 5 ⇒ 4(3) + 5 = 12 + 5 = 17