Question 192101
4*7=28 m^2 is the original area.
(4+x)(7+x)=2*28
28+11x+x^2=56
x^2+11x+28-56=0
x^2+11x-28=0
{{{x = (-b +- sqrt( b^2-4*a*c ))/(2*a) }}} 
x=(-11+-sqrt[11^2-4*1*-28])/2*1
x=(-11+-sqrt[121+112])/2
x=(-11+-sqrt233)/2
x=(-11+-15.26)/2
x=(-11+15.26)2
x=4.264/2
x=2.132 meters is the increase needed to double the garden size.
Proof:
(4+2.132)(7+2.132)=56
6.132*9.132=56
56~56