Selecting Specific Data By Dates

I would like to quantify quarterly data. My formula is currently set to identify a specific date registered, and then sum up all numbers by that date. For example, if the specified date is "7/25/16" all data for that date is automatically added together. However, I'm not sure how to set up the function so that it reads all dates in this quarter. Attached are screen shots/dummy copies for better understanding. Thank you!