how to solve this? which number replaces the question mark?

similar to above, but the numbers aren't required to be the sum of next, etc. simply all 3 numbers with the value for their alphabetical order is the same as the sum of the numbers around them. in this case:
34 PJH x
34+x=P+J+H
34+x=16+10+8
34+x=34
x=0

6F KM 24 (K = 11 and M = 13)

12L UC 24 (U = 21 and C = 3)

20RB I9 (I = 9)

4D GQ 24 (G = 7, Q = 17)

34 (P = 16 J = 10 H = 8) (? = 0)

A 1
B 2
C 3
D 4
E 5
F 6
G 7
H 8
I 9
J 10
K 11
L 12
M 13
N 14
O 15
P 16
Q 17
R 18
S 19
T 20
U 21
V 22
W 23
X 24
Y 25
Z 26

6 FKM 24 >>>
F=6 & K=11, M=13 K+M=24
1ST NUMBER IS 1st letter's value.
2nd number is sum of next two letters.

So, ? = J+H = 10+8=18.................Answer