12 lawns/9 hours = 1.33 lawns per hour
        
                    
             
        
        
        
<span>20-9x=11
-9x=11-20
-9x= -9
x= -9/(-9)
x=1
 4(2x+1)=8
2x+1=8/4
2x+1=2
2x=2-1
2x=1
x=1/2
x=0.5
 5(2x+5)=-15
2x+5= -15/5
2x+5= -3
2x= -3-5
2x= -8
x= -8/2
x=-4
3(8x+1)=-21
8x+1= -21/3
8x+1= -7
8x= -7-1
8x =-8
x= -8/8
x= -1
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2x + 3x = 100
5x=100
x=100/5
x= 20
 Therefore, 2x=2×20=40
 3x=3×20=60 
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