9514 1404 393
Answer:
y = 15·2.1599^x
Explanation:
We know that the number changed by the ratio 1523/15 = 101.5333... in 6 days, so the daily multiplier is the 6th root of this:
b = 101.5333...^(1/6) = 2.1599 . . . rounded to 4 dp
Of course, the coefficient 'a' in the equation is the initial number, 15.
Your exponential equation is ...
y = 15·2.1599^x
a = 15
b = 2.1599