Answer:
a is the perimeter which is given as 820 mm.
Explanation:
Perimeter, P = 820 mm
Length is 100 m less than twice of width
let the length is x and the width is y.
So,
x = 2 y - 100
P = 2 (x + y)
820 = 2 (2y - 100 + y)
410 = 3 y - 100
3 y = 510
y = 170 mm
x = 2 x 170 - 100 = 240 mm
The equation is
2 x = 2 y = a
where, a is the perimeter which is given as 820 mm.