Calcualte values in a range of cells to total an equal value in another cell

Firstly hi as this is my 1st post

I have attached a small part of an sheet i am using to help my planning at work

In Cell H5 i have a value which needs entering into F6:F20

The value in H5 for the example is 6,900 and i want to spread this out in F6:F20 based on the values in G6:G20

for example i have a value in G18 of 4,000 so i want F18 to equal 4,000 then G17 and G16 have 0 value so F17 and F16 have 0 values. G15 has a value of 2250 so F15 should have this value.

Now this means i have used 6250 of the 6,900 i have available.

So G14 equals 960 but F14 can only = 650 as thats all i have left. the every value in f needs to be 0 as there is nothing left to allocate

any help will be appreciated because everything i try ends up in a circular ref

thank you

stuart