I’ve been able to figure out the rest of the questions but this one has me stumped. I need to solve for x. Can someone please write the steps down so I can learn what to do?

Answer:
X= -11
Step-by-step explanation:
Combine the two equations to equal a supplementary line
(X+91)=(x+111)=180
Solve for x by reversing the equation
(x)+(x)=(180-91)+(-111)
x=-22/2
x=-11
then check it