Question

Phytoremediation is the use of plant growth to purify pollutants from soil, water, or air. Suppose that a crop of brake ferns can remove 151515 milligrams (\text{mg})(mg)left parenthesis, m, g, right parenthesis per square meter of a particular pollutant from the soil in 202020 weeks. After 202020 weeks, the ferns are harvested and a new crop is planted. If ccc represents the number of crops of brake ferns needed to phytoremediate soil contaminated with 170\,\text{mg}170mg170, space, m, g per square meter of the pollutant down to healthy levels of 5\,\text{mg}5mg5, space, m, g per square meter, which equation best models the situation? Choose 1 answer: 170-20c=5170−20c=5170, minus, 20, c, equals, 5 170+20c=5170+20c=5170, plus, 20, c, equals, 5 170-15c=5170−15c=5170, minus, 15, c, equals, 5 170+15c=5170+15c=5170, plus, 15, c, equals, 5

Answer 1

Equation that best models the situation is
`170-15c=5` where c = 11

Explanation:

Let the number of crops needed to remove pollutant = c

Since, 1 crop can remove 15 mg per sq. meter of pollutant.

Then, 'c' number of crops can remove '15c' mg per sq. meter of pollutant.

Now, the total amount of pollutant per sq. meter = 170 mg

And, it is required to bring the pollution level to 5 mg per sq. meter.

So, the equation representing the situation is given by,

Total amount of pollutant - Pollutants 'c' crops can remove = Amount of pollutant needed

i.e.
`170-15c=5`

Upon solving the equation, we get,

`170-15c=5\\\\-15c=5-170\\\\-15c=-165\\\\c=11`

Thus, equation that best models the situation is
`170-15c=5` where c = 11

Answer 2

An appropriate model is ...
170 - 15c = 5, c = 11

_____
All of your answer choices here show c=5, which is incorrect.