Answer:  54 mph
Step-by-step explanation:
d-the distance
s+9  -  the speed to the conference
d=6*(s+9)
s- is the speed on the way back home
d=7*s
so    6*(s+9)=7*s
        6s+54=7s
      -6s          -6s
        54= 7s-6s
        s=54  mph
 
        
             
        
        
        
11 of the 329.99 lawn mowers and 19 of the 249.99 lawn mowers
        
             
        
        
        
ah, those are systems you want one variable to cancel out. I would time the bottom equation by -1 so x cancels then u solve for y. then u plug all back in to solve for x.
 
        
             
        
        
        
Put this in your calculator or use pictures if you'd like. (3/4) x 12 and you'll get 9