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\mathrm{f}^{\prime}(\mathrm{x})=\mathrm{D}\left(\frac{1}{3}\left(64+\mathrm{x}^{2}\right)^{1 / 2}+\frac{1}{5}(10-\mathrm{x})\right)=\frac{1}{3} \frac{1}{2}\left(64+\mathrm{x}^{2}\right)^{-1 / 2}(2 \mathrm{x})-\frac{1}{5}=\frac{\mathrm{x}}{3 \sqrt{64+\mathrm{x}^{2}}}-\frac{1}{5}