Adding up ranges depending on condition

Dear all,

I am trying to build a table that sums up estimates depending on conditions.
More specifically, column B provides estimates of how long it will take my team to complete certain tasks.
Columns C and D are checkboxes corresponding to week 1 and week 2 accordingly.
What I need to do is sum up the estimates on column B separately for weeks 1 and 2 so that I can say we'll work 40 hours this week and 50 the next one.

I am under the impression that this can be achieved using arrays but I'm not sure how.
Please see attached spreadsheet

Can you help?
Cheers