We need to start from the innermost parenthesis and work our way out.
The first parenthesis is 
. These are not like terms because one involves a variable, while the other is a constant term. Two terms are summable if they involve the same power(s) of the same variable(s).
So, we can take one step outwards, and we arrive to the square brackets. We have
and 2z and -13z are like terms, so we can sum them:
Finally we arrive to the whole expression, which is
Because, again, 5z and 11z were like terms.
2.Alternate Interior angles theorem.
They given angles are alternate and interior when compared to each other, so they are congruent.
3 Vertical angles theorem.
The two angles are vertical angles and are not congruent.
4 Angle-Angle Similarity Postulate.
Because there are two corresponding angles that are congruent they are similar triangles by the angle-anlge similarity postulate.
To help you with it, plug-in 15 in each equation and see what you get!
