$x$ rays with a wavelength of $87\mathrm{.}0pm$ are directed onto a gold foil and eject tightly bound electrons from atoms of the foil. The ejected electrons then move in circular paths of radius $r$ in a region of uniform magnetic field with magnitude vec$(B).$ For the fastest of the ejected electrons, the product $Br$ is equal to $1\mathrm{.}90{10}^{-4}T*m.$ Find $($a$)$ the maximum kinetic energy of those electrons and $($b$)$ the work done in removing them from the gold atoms.

$($a$)$ Number

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$($b$)$ Number

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