If 8,6,2=4; 12,5,8=15; 13,10,x=18 then what would be x?

Question

IF
1,3,3=5
9,7,4=8
11,14,10=15
20,16,12=18
Than
3,6,7=?

Answer 1

If 8,6,2=4; 12,5,8=15; 13,10,x=18 then what would be x?

8-6+2=4;
12-5+8=15;
13-10+15=18.
so X=15.

Answer 2

15

a,b,c=d a+c-b=d

13+15=28-10=18

Answer 3

8-6+2=4
12-5+8=15
13-10+15=18
SO X=15