hELP~ gr. 11 math = exponential growth ><?

Question

ok ~ do u guys know how to solve this:

40=100( 0.88) ^ n

solve "n" ~ = . =

ummm-

i need the Hand doing way ( do u guys mind explain?)



also show me the calculator way if u can ^___^

THX U~

Answer 1

Take log of both sides
log(0.4) = n*log(0.88) so

n= log(0.4)/log(0.88) =7.168

Answer 2

40=100(.88)^n

2/5=.88^n
ln(.4)=(n)ln(.88)
ln(.4)/ln(.88)=n