Explanation: width যদি x হয় Length = 4x area = \(4x^{2}\) এর perimeter = \(2(x+4x)=10x\) 20 Tk / sq.mt করে মোট খরচ = 1280 Tk অর্থাৎ মোট area = \(\frac{1280}{20} = 64\) sq.mt অতএব, \(4x^{2}=64 \Rightarrow x^{2}=16 \Rightarrow x=4\) \(\therefore\) Perimeter = \(10x = 40\) meters]