Question 332644
Let us assume the width as x so  and length as 4+x
given area =21 sqm
 area =length *width
21= (4+x)* x
21=4x+x^2
we can change this eqaution into standard form
x^2+4x-21=0
now factor this eqaution
x^2+4x-21=0
x^2+7x-3x-21=0
x(x+7)-3(x+7)
(x-3)(x+7)=0
x=3,-7
since wehave to calculte the area we have to consider only the positive value of x
x=3


checking
x=3
21=(x+4)*x
21 =3+4*3
21=7*3
21=21
x=-7
21 =(-7+4)*3
21 =-3*3
21  notequal to -9