Answer:
July 1st
Step-by-step explanation:
Find the least common multiple of 6 and 10. The LCM of 6 and 10 is 30, meaning 30 days after June 1st, you and your brother will be off from work. Add the first day of June to an extra 30 days, that will leave you at July 1st.
June 1st + 30 days
July 1st