Question 446178
5m+n=23 
m-9n=69 

n=-5m+23 
m-9n=69 

n=-5m+23 
m-9(-5m+23)=69 

n=-5m+23 
m+45m-207=69 

n=-5m+23 
46m-207=69 

n=-5m+23 
46m=207+69 

Add 69 to 207 to get 276. 

n=-5m+23 
46m=276 

n=-5m+23 
 
n=-5m+23 
m=6 

n=-5(6)+23 
m=6 

n=-30+23 
m=6 

Add 23 to -30 to get -7. 

n=-7 

m=6 

n=-7 

m=6