Let $\>l\>$ be the length of a diagonal of a rectangle whose sides have lengths $\>x\>$ and $\>y\>$, and assume that $\>x\>$ and $\>y\>$ vary with time.
If $\>x\>$ increases at a constant rate of $\> \frac {1} {3}\>$ ft/s and $\>y\>$ decreases at a constant rate of $\> \frac {1} {6}\>$ ft/s, how fast is the size of the diagonal changing when $\>x = 2\>$ ft. and $\>y = 8\>$ ft?

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