(21+39a)/20. Because they have to have the same denominator
        
             
        
        
        
-25 + 2 = -23  and...   -25 × 2 = - 50
hope that helps :D
 
        
             
        
        
        
Answer:
90 and 30 liters
Step-by-step explanation:
1) if solution of 20% is 'x' and of 60% is 'y' liters, then
2) the pure chlorine is: for solution of 20% - 0.2x, for solution of 60% - 0.6y and 
3) the mix of the two solutions is 120=x+y.
4) using these items it is possible to make up the system of two equations:

5) finally, x=90 liters of 20%; y=30 liters of 60% solution.
 
        
             
        
        
        
Answer: 2 over 1
Step-by-step explanation:
1+1=2
However we want this as a fraction
Any whole number as a fraction is just over one
Therefore the final answer is 2 over 1
You’re welcome Kaeya!