Half of my brother's four-day work is one-eighth of my brother's one-day work; From this, it can be concluded that the remaining half-brother completed three-eighths of the total workload in three days, so the elder brother completed seven-eighths in seven days, that is, the workload that the younger brother completed in the next three days was one-eighth of the total workload. From this, it can be concluded that the younger brother completed one-fourth of the total workload every day, so it takes him 24 days to do this work alone.

The second problem can't be solved without an equation now.