sort by function

[asa man]

Hi
I have below table

AT	PT	FT
	5	12
8	6
10	2
12	4
13	3
22	4

<tbody>
</tbody>

I want to find smallest PT that AT belonged PT <= FT ,
then founded PT + FT(old)=FT(new)
and founded PT ignore in next row calculation,
and repeat trend in every row whit excel function.
for example
FT=12
AT<=12:{8,10,12}
PT: {6,2,4}
FT(new)=2+12=14


FT=14
AT:{8,12,13}
PT:{6,4,3}
FT(new)=3+14=17

AT	PT	FT
	5	12
8	6	14
10	2	17
12	4
13	3
22	4

<tbody>
</tbody>