Answer:
1) The store selling for 1.1 per 3 lbs
2) $6.24
Step-by-step explanation:
1)
1.1/3 = 0.37
0.78/2 = 0.39
0.37 is cheaper so it's a better deal
2)

So, here we have an exponential function.
Remember that an exponential function has the form:

Where a represents an initial amount, and r is the rate of this amount to change. (Increase, or decrease).
So, given that the population of City A in 2000 was 40 thousand people and the population increased by 13% each year, we can say that

So,

For city B:

But something different happens with city C. This is not an exponential function, this is a linear function.
So,

Subtract 12x from 84x = 72x