If you are working with time or days, you can't put in a negative value because if you are doing an experiment, you can't go back in time to do that experiment to gather data. (Time for the most part considered to be an input value so that's why I used it as an example.)
Y=x+1 would be the best equation that represents the line
Answer:
7 . time os on axis X. total vector lenght is 7.
In the old aquarium, 3 tablespoons of salt were used for 20 gallons. That's a conversion ratio of
![\dfrac{3\,\rm tbsp}{20\,\rm{gal}}=0.15\,\dfrac{\rm tbsp}{\rm gal}](https://tex.z-dn.net/?f=%5Cdfrac%7B3%5C%2C%5Crm%20tbsp%7D%7B20%5C%2C%5Crm%7Bgal%7D%7D%3D0.15%5C%2C%5Cdfrac%7B%5Crm%20tbsp%7D%7B%5Crm%20gal%7D)
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
![(50\,\rm{gal})\left(0.15\,\dfrac{\rm tbsp}{\rm gal}\right)=7.5\,\rm{tbsp}](https://tex.z-dn.net/?f=%2850%5C%2C%5Crm%7Bgal%7D%29%5Cleft%280.15%5C%2C%5Cdfrac%7B%5Crm%20tbsp%7D%7B%5Crm%20gal%7D%5Cright%29%3D7.5%5C%2C%5Crm%7Btbsp%7D)
to maintain the salinity.
I think it's 1/2 because 5/10= 1/2
I hope this helps!