Are E and R both just variables or is E really the number e ???
If there are 2 variables then you can't solve it with just one equation.
However ,if your question to find R given this then..
log(e) = 1.2 + 1.81 ln(R)
1= 1.2 + 1.81 ln(R)
-0.2= 1.81 ln(R)
(-0.2/1.81)= ln(R)
R=e^(-0.2/1.81)
e^(-0.2/1.81) = 0.8953888036358034