Question

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Answer 1

Notice that:

$\measuredangle ABC=\measuredangle1+\measuredangle DBC$

Solving for angle 1 we get:

$\measuredangle1=\measuredangle ABC-\measuredangle DBC$

Substituting the measure of angles ABC and DBC we get:

$\begin{gathered} \measuredangle1=135^{\circ}-75^{\circ} \\ \measuredangle1=60^{\circ} \end{gathered}$

The measure of ∡1 is 60 degrees.