math word problem

Question

The half-life of radioactive strontium-90 is approximately 31 years. In 1961, radioactives strontium-90 was released into the atmosphere during testing of nuclear weapons, and was absorbed into people's bones. How many years does it take until only 6 percent of the original amount absorbed remains

Answer 1

0.06a₀ = a₀(0.5)^t/31

0.06 = 0.5^t/31

ln 0.6 = (t/31) ln 0.5

 

Can you solve for t and answer?