Tolong dibantu nomor 15 16 dan juga 17 tolonglah pls

15. BC = 15
DC = 9
DE = 6
FE = 10
K = AB+BC+CD+DE+EF+FA
K = 8+15+9+6+10+12 = 60

16. 3x+7 = 31-x
3x+x = 31-7
4x = 24
x = 24/4 = 6

17. 2x-4 = 12
2x = 12+4
x = 16/2 = 8
x+2 = 8+2 = 10