Respuesta :

y = 36
Steps:
54 - y = 18
Subtract 54 from both sides
54 - y - 54 = 18 - 54
Simplify 
-y = -36
Divide both sides by -1
-y / -1 = -36 / -1
Simplify
y = 36

Hope this helps you! (:
-Hamilton1757