Area of rectangular courtyard is = length x breadth

$Given l:b = 6:5$

$i.e. \frac{6}{5} = \frac{6}{5}$

$l = \frac{6}{5}b$

$3000 = \frac{6}{5}bxb$

$\frac{15000}{6} = b^{2}$

$2500 = b^{2}$

$b = 50$

$l = \frac{6}{5}b = \frac{6}{5}x50$

$l = 60$

Perimeter of rectangular courtyard is = 2(l+b)

= 2(60+50)

220m