Euclidean Geometry: Interior Angles and Circular Arc Relationships

In the diagram, \(O\) is the centre of the circle through \(A\), \(B\), \(C\) and \(D\) and \(TB\) is the tangent to the circle at \(B\).
The diameter \(AC\) and the chord \(BD\) intersects at \(X\).
Given \(\angle DCX = 32{}^\circ\) and \(\angle OBC = 40{}^\circ\), calculate, stating your reasons clearly,

1. \(\angle OAB\),
2. \(\angle CXD\),
3. \(\angle ABT\),
4. \(\angle BAD\).