After 62.0 hours , 1.0 g remains unchanged from a sample of 42k . how much 42k was in the original sample?

The half-life of K-42 is 12.360 hours.

62 hours is just about 5 half-lives, so we'd expect about 1/32 of the original amount to remain after that time. (32 = 2^5)

In fact, it's 12.36 / 62 = 5.016 half-lives.

2^5.016 = 32.36

So if you started with 32.36g in the original sample, it would have decayed down to 1g after 5.016 half-lives.

astronomers such as edwin hubble.