formula for decreasing monthly total budget by weekly sums

Hello all,

I can't figure out how to create a formula that shows two factors in a monthly budget; 1. a decreasing monthly budget total by weekly amounts (I completed part 1., see below), 2. the weekly amount cells divide the budget balance equally between the four weeks. As expenses are entered in "week 1," the remaining three weeks equally distribute the remaining budget balance. The same step happens when "week 2" expenses are entered thru "week 4" which then leaves either a zero, negative, or surplus budget balance.

Produce
Week 1 Week 2 Week 3 Week 4 Budget Balance Monthly Budget
$20.00 $100.00 $140.00 $140.00 $280.0 $400.00

Thank you,
Poundian