Check iny' work

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Required information

To study the physical features of Hydra viridis, a student uses a compound microscope with a magnifying power of $423.$

If the eyepiece has focal length $1\mathrm{.}70cm$ and the tube length is $17\mathrm{.}7cm,$ what focal length does the objective have? Assume a near point of $25\mathrm{.}0cm.$

$mm$