Sagot :
l = 8 + w ;
l * w + 160 = ( l + 2 ) * ( w + 2 ) => l * w + 160 = l * w + 2 * l + 2 * w + 4 => 156 = 2 * ( l + w ) => 78 = l + w; but, l = 8 + w => 78 = 8 + 2 * w => w = 70 / 2 => w = 35 feet; l = 8 + 35 => l = 43 feet.
l * w + 160 = ( l + 2 ) * ( w + 2 ) => l * w + 160 = l * w + 2 * l + 2 * w + 4 => 156 = 2 * ( l + w ) => 78 = l + w; but, l = 8 + w => 78 = 8 + 2 * w => w = 70 / 2 => w = 35 feet; l = 8 + 35 => l = 43 feet.
[tex]the\ fish\ pond:\\A_p=x\cdot (x+8)=x^2+8x\\\\the\ area\ covered\ by\ the\ walk:\\A_{w}=(x+2\cdot2)\cdot(x+8+2\cdot2)=(x+4)(x+12)=x^2+16x+48\\\\A_w=A_p+160\ \ \ \Rightarrow\ \ \ \ x^2+16x+48=x^2+8x+160\\\\16x-8x=160\ \ \ \Rightarrow\ \ \ 8x=160\ \ \ \Rightarrow\ \ \ x=20\\\\Ans.\ the\ width\ of\ the\ fish\ pond\ is\ 20\ ft\ and\ the\ length\ is\ 28\ ft[/tex]