Answer:
X = 180 + -1Y
Explanation:
X + Y = 180 
 
Solving for variable 'X'. 
 
Move all terms containing X to the left, all other terms to the right. 
 
Add '-1Y' to each side of the equation. 
X + Y + -1Y = 180 + -1Y 
 
Combine like terms: Y + -1Y = 0 
X + 0 = 180 + -1Y 
X = 180 + -1Y 
 
Simplifying 
X = 180 + -1Y