# Angles A and B are supplementary.If mangle A= 78° what is mangle B?

Angles A and B are supplementary.
If $m\mathrm{\angle }A=78°$ what is $m\mathrm{\angle }B$

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Latisha Oneil

The measures of supplementary angles add up to ${180}^{\circ }$. So if $m\mathrm{\angle }A={78}^{\circ }$, then the measure of angle B must be $m\mathrm{\angle }B={180}^{\circ }-m\mathrm{\angle }A={180}^{\circ }-{78}^{\circ }={102}^{\circ }$