The length of a rectangle is 6 meter less than twice its width. the area of the rectangle is 140m square. what are the dimensions of the rectangle

Hello : 
x : the lenghe    y : the width
x-6 = 2y(1)
xy=140(2)
by (1) : x= 6+2y
subsct in (2) :  (6+2y)y =140
2y² +6y -140 =0
y² +3y -70 = 0
delta : b²-4ac    a=1   b=3   c= -70
3²-4(1)(-70) = 289=17²
y1 = (-3-17)/2  negatif... refused
y2 = (-3+17)/2 = 7
x= 6+2(7) = 20