The answer to your question would be 150 (c)
        
             
        
        
        
Can you retype this? It's kind of hard to understand what you are saying
        
             
        
        
        
In the old aquarium, 3 tablespoons of salt were used for 20 gallons. That's a conversion ratio of

That is, for every gallon of water in the aquarium, there was 0.15 tbsp of salt. So a 50 gallon aquarium, Ill should add

to maintain the salinity.
 
        
             
        
        
        
Answer: The net change would be -2.
Step-by-step explanation: The upward change of elevator is represented by positive sign while the downward change represented by negative sign.
Given, First the elevator goes up 15 floors, change = + 15, Then it goes 9 floors down, change = -9, Then it goes 11 floors up,Change = + 11, Finally, it goes 19 floor down, Change = - 19 So, the net change = sum of total changes = 15 - 9 + 11 - 19 = -2 
your welcome!