The most reasonable would be grams.
The general formula for exponential growth and decays is:

if k>0 then then it is an exponential growth function. If k<0 then the function represents an exponential decay.
Now we need to classify each of the functions:
1.
The function

can be wrtten as:

comparing with the general formula we notice that k=2, therefore this is an exponential growth.
2.
The function

can be written as:

comparing with the general formula we notice that k=-4, therefore this is an exponential decay.
3.
The function

comparing with the general formula we notice that k=-1, therefore this is an exponential decay.
Answer:
Common Ratio=1/3
Step-by-step explanation:
X - y = 5,
x = 5 + y
substitute (x = 5 + y) into the first equation,
5 + y + 2y = -1
3y = -6
y = -2,
substitute y = -2 into (x - y = 5),
x + 2 = 5
x = 3
Hence, x = 3, y = -2
C represents the cost. R represents the number of rooms.
C=50 + 12R