Question 774156
n1 + n2 = 180
n2 = 12 + 3(n1)
 

n1 + n2 = 180
n1 + 12 + 3n1 = 180
4n1 + 12 = 180
4n1 = 180 - 12
4n1 = 168
4n1 / 4 = 168 / 4
n1 = 42 degrees ans.

n2 = 12 + (42)
n2 = 138 degrees ans.

checking:

n1 + n2 = 180
42 + 138 = 180
180 = 180