Is there a function that will spread a value across other values based on that value. Example below :

Original Value
Week1 100
Week2 200
Week3 400
Total 700

Value to spread across the 3 weeks 350
The 350 split would give
Week1 50
Week2 100
Week3 200
Total 350

Therefore new value would be
Week1 150
Week2 300
Week3 600
Total 1050

Hope that's clear