Half life of dimes

Question

If half of the dimes in the United States disappear every 37 years –
and are not replaced – how long will it take for the 4.2 billion dimes
minted last year to be virtually all gone?

Answer 1

1 = 4.2(0.5)^t/37

0.238 = 0.5^t/37

ln 0.238 = (t/37) ln 0.5

 

Can you solve for t and answer?