# How to do this

$\frac{{7}^{21}+\hspace{0.17em}{7}^{22}+\hspace{0.17em}{7}^{23}+\hspace{0.17em}{7}^{24}}{25}=\frac{{7}^{21}(1+7+\hspace{0.17em}{7}^{2}+{7}^{3})}{25}=\frac{{7}^{21}*400}{25}\phantom{\rule{0ex}{0ex}}\because 400isdivisibleby25,sotheremainderiszeroforthewholeexpression.$

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