If the width of the uniform shaded portion is x m; its area in terms of x is :

1. 320 m² - (16 - 2x)(20 - 2x) m²

2. 320 m² - (16 - x)(20 - x) m²

3. 320 m² - (16 - 2x)(20 - x) m²

4. 320 m² - (16 - x)(20 - 2x) m²

From figure,

EF = 16 - x - x = (16 - 2x) meters

FG = 20 - x - x = (20 - 2x) meters

Area of shaded portion = Area of rectangle ABCD - Area of rectangle EFGH

= AB × BC - EF × FG

= 16 × 20 - (16 - 2x)(20 - 2x)

= 320 m² - (16 - 2x)(20 - 2x) m².

Hence, Option 1 is the correct option.