To find out how much Mr. Chen spends on coffee in 30 days, you can multiply the cost of one coffee by the number of days:
Cost of one latte = $3.50
Number of days = 30
Total cost = Cost of one latte × Number of days
Total cost = $3.50 × 30 = $105.00
Therefore, it costs Mr. Chen $105.00 to buy coffee every 30 days.