It would be the first answer. Bubble. I don't know what you call it. But yeah, it's the first one.
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,

Let the number total slices = x
He ate (1/4) x
He has x - 1/4 x = 3/4 x slices left.
Each one of these slices is cut into 1/8s
T (total number of slices) = 8 * (3/4x)
T = (8*3/4) x
T = (24/4)x
T = 6x slices.