the perimeter is the sum of all a shapes sides.
so if length is two times the width, you could write it as 2w.
2w + 2w + w + w = 42. Simplified, it's 6w = 42.
Divide both sides by 6, and you get w = 7.
Since the length is 2w, 2 * 7 = 14, so the length is 14
Area of rectangle is length * width, so do 14 * 7 which is 98. Slap on some units and your answer is 98 sq m