Abiologist tracks the numbers of bacteria living in a water tank. the biologist used a function that represents the amount of a certain chemical solution that is added to the water.
-when the water has no chemicals, the number of bacteria (b) is 1200 per gallon.
-for each tablespoon of the chemical solution (c) added to each gallon of water. the number of bacteria decreases by 75 per gallon.
how much of the chemical, in tablespoons, must be added to a 500-gallon tank to reduce the bacteria count to a safe 300 bacteria per gallon?

A biologist tracks the numbers of bacteria living in a water tank. the biologist used a function that represents the amount of a certain chemical solution that is added to the water.
data gathered:
water has no chemicals-- number of bacteria (b) is 1200 per gallon
tablespoon of the chemical solution (c) added to each gallon of water--number of bacteria decreases by 75 per gallon.
question:
How much of the chemical, in tablespoons, must be added to a 500-gallon tank to reduce the bacteria count to a safe 300 bacteria per gallon?

since a tablespoon of chemical solution reduces bacteria to 75 per gallon, then 12 tablespoons should be added to every gallon of water in the 500 gal tank to reduce bacteria to a safe 300 bacteria/gall.
here's how we got 12.
4 x 75 = 300

since we have to reduce the bacteria to a safe 300/gal we will have to eliminate the 900 bacteria/gal where: 1200-300 = 900
and 900÷75(equivalent to 1 tablespoon/gal)= 12. Therefore we have to add 12 tablespoons to each of the gallon of water. 

The correct answer is d. (0,5)