W=width of the pasture, and <span>320000/w=length (parallel to river) </span> <span>F=twice width + length </span> <span>=2w + 320000/w </span>
<span>Find derivative of F with respect to w and equate to zero to find w. </span> <span>i.e. </span> <span>Solve for w in </span> <span>dF/dw=0 hope it helps</span>
