4. Solve for x, and explain which theorem or
postulate that helps you find the answer.

Answer:
x = 4° Alternate Exterior Angles
Step-by-step explanation:
[tex]\begin{array}{cc}Statement&Reason\\21x + 6= 90&Alternate -Exterior -Angles\\\end{array}\right][/tex]
Solve for x:
21x + 6° = 90°
21x = 84°
x = 84°/21
x = 4°
[tex]\begin{array}{ccc}Statement&Reason\\21x + 6= 90&Alternate -Exterior -Angles\\x = 4&Algebra\end{array}\right][/tex]
-Chetan K