y = x - 3
1. Subtract 7 from the right to the left.
* 4y = 4x - 12
2. Divide the 4 (constant) next to the 'y' to the other side.
* y = 4/4x - 12/4 
* y = x - 3
        
             
        
        
        
I also agree with answer C
        
             
        
        
        
I'm assuming the funds earn 5% yearly?
Call x the amount he saves every year.  The first year's deposit will be multiplied by 1.05 three times, the next will be multiplied by 1.05 twice, the third will be multiplied by 1.05 once, and the fourth will not generate interest (as it will immediately be used to buy the car).
Therefore, x(1.05^3+1.05^2+1.05+1)=21000, so 4.31x=21000.  Dividing by 4.31, we see that x is approximately equal to 4872.
        
             
        
        
        
Any number over its self. for example 1,999/1,999
        
             
        
        
        
The standard form is 3x+4y=8