we are given
[tex] S=3r^{4t} [/tex]
Since, we have to solve for t
so, we will isolate t on anyone side
divide both sides by 3
[tex] \frac{S}{3} =r^{4t} [/tex]
now, we can take ln both sides
[tex] ln(\frac{S}{3}) =ln(r^{4t}) [/tex]
we can simplify it
[tex] ln(\frac{S}{3}) =4tln(r) [/tex]
divide both sides by 4ln(r)
[tex] t=\frac{ln(\frac{S}{3})}{4ln(r)} [/tex]..............Answer