All you have given is an expression..... T can be any value....
if you have an EQUATION like 4500 = e^(-20000/(1.987T) take the ln of both sides of the equation and you have
ln 4500 = -20000/(1.987T) then re-arrange
1.987T = -2000/4500 then divide both sides by 1.987
T = -20000/(4500(1.987))
1.815 x 10^11 / 8.67 x 10^22 = .20934x 10^-11 = e^-20000/1.987T
-26.892 =- 20000/1.987T
T = -20000/(1.987(-26.892) T =374.29