The doctor prescribed 30 ml of fever syrup for Chris. He had to take 5 ml of the fever syrup every 3 hour. He first took his fever syrup at 4 a.m. When would his last intake be?

1. Calculate the total number of doses Chris needs to take.

Total doses = $30 \div 5 = 6$

2. Determine the number of time intervals between the first and last dose.

Number of intervals = $6 - 1 = 5$

3. Calculate the total time elapsed from the first to the last dose.

Total time elapsed = $5 \times 3 = 15$ hours

4. Find the time of the last intake.

Time of last intake = 4 a.m. + 15 hours = 7 p.m.