Answer:
12
Step-by-step explanation:
Then the -12 and +12 will cancel out, so you're left with a clean isolated r on the left:
r -12 +12 = 19 + 12
r = 31
143
180 - 37 = 143.
We know this because y + 37 = 180
so we can does 180-37 to get our answer.