Problem to calculate target price according to tree levels

[tommy1234]

Hello
i have 2 problems that i can't find a solution for them.
i attached an excel file which contain 3 columns:
Column 'A' - item level (small number represent higher stage on product tree)
Column 'B' - item name
Column 'C' - single item price
Column 'D' - accumulated price according to the levels.
for example : line 9 is the sum of line 10 and line 10 is the sum of lines 11-12
Column 'E' - in this column i want to enter a target price in which all the levels below it should be exactly 280.
Column 'F' - example to the problem i have in my code => this is the place where i need help #1 !!!
Column 'G' - example to the calculation of the new price (Column 'F')
another problem will be if the user is going to put another target price in low level, like in line 19, he will put 25, how can i answer to that ? #2
Pls, its urgent

Thanks

[Aussiebear]

another problem will be if the user is going to put another target price in low level, like in line 19, he will put 25, how can i answer to that ? #2

Use Data Validation, and set a minimum price level

[tommy1234]

who can assist me to fix my code ?
can someone help me with the first problem ?