Can you find the half-life of tritium mathematicaly?

Question

This is from Chapter 9, Exercise 9-4, #39 of Fundamentals of Technical Mathematics (2nd edition): In Example 9-3 the half-life of tritium was determined graphically to be approximately 12 years. Using the formula for radioactive decay m = m0e^-kt, where k = 0.055 per year for tritium, find the half-life of tritium mathematically. Let m/m0 = 0.5 and solve for t.

Answer 1

m/m0 = e^(-kt)
0.5 = e^(-0.055t); taking logarithm to base e on both sides,
ln 0.5 = - 0.055t
t = -(ln 0.5/ 0.055)
= -(-0.6931/0.055)
= 12.6 years