The rate of change is just the slope. it is the. hange in y du used by the change in x since we have the points (1,15) and (2,30) we have

so it is D. it is not when do you use a fraction and when a whole number. it will always be a fraction but sometimes this will reduce to a whole number.
48.72 is number 12 if that is what your asking for
I have attached the graph so you can compare but it is graph C.
Hope that helps.
Answer:
x = 8
Step-by-step explanation:
log₅ (10x − 1) = log₅ (9x + 7)
10x − 1 = 9x + 7
x = 8