Question

Need help with this one question, please also try to explain.

Answer 1

m<ABC + m<CBD = m<ABD

m<ABD = 85 and m<CBD = x

m<ABC + x = 85

m<ABC = 85 - x

Answer 2

<ABC + <CBD = <ABD

substitute <ABD = 85 and <CBD = x

<ABC + x = 85