Mmmmm.....OK.......I didn't see the words " yearly % percent drop" anywhere in the question......!!!
Here's how to solve this :
9.3 = 22 (1 - r)^14 where r is the percent decrease [ in decimal form] per year
Divide both sides by 22
9.3 / 22 = (1 - r)^14
Take the log of both sides :
log (9.3 / 22) = log (1 - r)^14
And by a log property, we can write :
log (9.3 / 22) = 14 * log (1 - r)
Divide both sides by 14
log (9.3 / 22) / 14 = log (1 - r)
And....in exponential form we have
10^ [ log (9.3 / 22) / 14 ] = 1 - r
Rearrange
r = 1 - 10^ [ log (9.3 / 22) / 14 ] = about 0.0596489... or about 5.96489% per year
