Take the ln of both sides
ln26.6 = .1722t+ ln18.5
(ln26.6 -ln18.5 ) / .1722 = t = 2.1088
Solve for t over the real numbers:
26.6 = 18.5 e^(0.1722 t)
26.6 = 133/5 and 18.5 e^(0.1722 t) = 37/2 e^(861 t/5000):
133/5 = 37/2 e^((861 t)/5000)
133/5 = 37/2 e^((861 t)/5000) is equivalent to 37/2 e^((861 t)/5000) = 133/5:
37/2 e^((861 t)/5000) = 133/5
Multiply both sides by 2/37:
e^((861 t)/5000) = 266/185
Take the natural logarithm of both sides:
(861 t)/5000 = log(266/185)
Multiply both sides by 5000/861:
Answer: | t = 5000/861 log(266/185)=2.108829......etc.