The rate of change is the slope.
That equation is (practically) in the form of y=mx+b because T(d) is very similar to y.
T(d) = 39.27d+36.77
y = mx+b
In this case, d would equal x. T(d) would equal y. 36.77 would equal b.
m is the slope, or the rate of change.
The rate of change is the variable, d, or the answer choice, a: the number of drinks purchased.
Answer:
Claire owed Martha $8 she originally owed Martha 12 but already gave her 4 this was a problem for Claire considering she only got $4 a week
In general an annual rate of

compounded monthly will multiply the amount by a factor of

each month.
Each month of 4.3% is a factor of

. That goes for five months, so is multiplied by itself five times, so gets a fifth power.
Each month of 13.7% is a factor of

. He pays this for 12-5=7 months, so it gets an exponent of seven.
We started the year owing $2600 of principal, so after the year we owe

.
Choice A.
It is B. the differences are added together