## Geometry: Common Core (15th Edition)

$m\angle ABC=85-x$
The Angle Addition Postulate says: $m\angle ABC + m\angle CBD = m\angle ABD$ Substitute the given values. $m\angle ABC + x=85$ Subtract x from each side to solve for $\angle ABC$. $m\angle ABC+x-x=85-x$ $m\angle ABC=85-x$