### Home > A2C > Chapter 5 > Lesson 5.2.3 > Problem 5-93

5-93.

Use the equation *y* = *ab ^{x}*.

*b* = multiplier = 3

*a* = starting point (today) = 72 million

What exponent should you use for 15 days before today?

If you aren't sure, think about a simpler problem: what would you use for yesterday? The day before that? Notice that *x* = 1 and *x* = 2 would represent tomorrow and the day after that.