A small factory produces two types of items, A and B. It takes 4 hours to produce one unit of item A and 6 hours to produce one unit of item B. The factory operates for a total of 120 hours per week. The relationship between the number of units of item A ($A$) and item B ($B$) produced is given by $4A+6B=120$. What is the maximum number of units of item A that can be produced if no units of item B are produced?