Answer
$2.21\times10^{-11}J$
Work Step by Step
$\Delta E=m_{m}c^{2}$
$m_{m}=270m_{e}=270\times 9.11\times10^{-31}kg$
Also, $c=3\times10^{8}$
Therefore, $\Delta E=270 \times9.11\times10^{-31}\times(3\times10^{8})^{2}$= $2.21\times10^{-11}J$
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