Given: 5+8ln(x)=15.8
Solution:
first solve for ln(x)
ln(x)=(15.8-5)/8 = 1.35
Next, using the definition of log_e(x) (or ln(x), or simply log(x))
log_e(x)=y ≡ e^y = x
This means that
log_e(x) = 1.35 ≡ x=e^(y)=e^(1.35) = 3.8574
or
x=3.86 (to the nearest hundredth)