here
p= 15000
r=15%
t= 3 yrs
now
depreciation = p(1-r/100)^t
= 15000(1-15/100)^3
=9211.875
=9212 or 9211.88
It’s 152y+125, basically by simplifying
I don't have an idea about the 1st one but second one goes by subtracting 1/3
subtract 1/3 from 8 1/3 it's 8, subtract 1/4 from 8 it's 7 2/3. figuring out the patterns are simple most of the time bu you can get stuck sometimes, if you wanna get better, practice...