Answer:
y = 21·0.7^x
Step-by-step explanation:
The pair (0, 21) tells you the multiplier is 21. (The exponential factor is 1 for x=0.)
Any adjacent pair of y-values can tell you the common ratio, hence the base of the exponential term. For example, using the y-values associated with x=0 and x=1, we find the base to be ...
... 14.7/21 = 0.7
Then the equation is ...
... y = multiplier · base^x
... y = 21·0.7^x
