Let the length of the rectangle be L and let the width of the rectangle be W.
It is given that the area of the rectangle is 98 cm^2
=> L*W = 98
The length is twice the width
=> L = 2W
This gives W*2W = 98
=> W^2 = 49
=> W = 7
L = 14
The length of the required rectangle is 14 cm and the width is 7 cm.