If the length of the rectangle is x, then we know the width is x + 1.
The area of a rectangle is length · width, so we can substitute as x · (x + 1)
Now, we now x · (x + 1) = 42
Expand
x² + x = 42
Solve
x² + x - 42 = 0
(x + 7)(x - 6) = 0
So, x = 6
That means the length is 6 meters and the width is 7 meters.