[solved]Sum Days into weeks

in column B, i have a list of days running (currently 1-30), starting at b2. in columns c and d i have data i would like to sum those totals into weeks of 7 in a single cell.

can anybody point me in the right direction for how to do this?

thank you for your help

edit: im working in google spreadsheets so sumifs cannot be used, however i have found alternative workarounds to sumifs statements so if i can at least get the workflow i can adapt as needed