Question 363729
First Equation:
M + N = 180

2nd Equation
M  = N/2 + 9

Substitute the value of M in Equation 2 to Equation 1

(N/2 + 9) + N = 180
N (1/2 + 1)   = 180 - 9
        3N/2  = 171
 
Multiply equation by 2/3

         N   = 2/3 (171)
         N   = 114

Since M + N = 180
        M    = 180 - N  
        M    = 180 - 114
        M    = 66

The angles are 66 & 114