We will use the property of logarithms that #ln(a^x) = xln(a)#
With that:
#3.14159^x = 4#
#=> ln(3.14159^x)=ln(4)#
#=> xln(3.14159)=ln(4)#
#:. x=ln(4)/ln(3.14159)#
Note that this is eqivalent to the base #3.14159# log of #4#, a result we could have also found by taking the base #3.14159# log of both sides and applying #log_a(a^x)=x#