Remember that
The area of a rectangle is equal to
A=L*W
In this problem
A=21 m2 ----> given
L=2W-1
substitute the given values in the formula of Area
21=(2W-1)*W
solve for W
21=2W^2-W
2W^2-W-21=0
Solve the quadratic equation
using a graphing tool
The value of W=3.5 m
Find out the value of L
L=2(3.5)-1
L=6 m
therefore
The dimensions are 6 m x 3.5 m
