Please help me I don’t understand I will mark as brainliest!!! Stay safe :)

Answer:
A) [tex]\frac{n+54}{9} =21[/tex]
[tex]n+54=21*9[/tex]
[tex]n+54=189[/tex]
[tex]n=189-54[/tex]
B) [tex]n=135[/tex]
C) Equation and Solution:
[tex]n+28=156\\n=156-28\\n=128[/tex]