You cannot do so. Too many unknowns.
PNode has 6 unknowns, but two are given, so only 4 true unknowns.
But you cannot solve for anything without the 6 unknown values of D. So up to 10 unknowns.
Oh, and del_node is completely unknown too. 5 more of them, so 15 unknowns in total.
The second set of equations, relating del_node to D, is of little help, since we can use that to essentially eliminate del_node.
One other point, the second set of equations is meaningless, since you tell us there are 5 elements of del_node. But the elements of del_node are simple ratios or L(i) and D(i). And since there are 6 values in L and D, that means you are trying to stuff 6 points of "stuff" into a 5 pound bag.
Regardless, you cannot solve the problem. No mathematics will give you an answer.
You need to spend some time re-thinking this problem.