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)=4 \, \mathrm{ft}, \frac{\mathrm{dr}}{\mathrm{dt}}=1 \, \mathrm{ft} / \mathrm{hr}, \mathrm{s}=12 \, \mathrm{ft}, \frac{\mathrm{ds}}{\mathrm{dt}}=3 \, \mathrm{ft} / \mathrm{hr}