Tolong jawab dengan cara yang lengkap

U2-u1 = u3- u2

(2k+ 16) – (3k+12) = (44-k) – ( 2k+16)
– k – 4 = -3k + 28
2k = 32
k = 12

urutan aritmatikanya :
3k + 12 , 2k+16, 44- k
3(12)+12,  2(12)+16 ,  44- 12
36 +12  ,  24 + 16 , 32
48, 40 , 32

b = 48-40 = -8

un= a + (n-1)b = 48+ (n-1)-8
    = 48 – 8n +8
   =56- 8n
  = 8 ( 7 – n) … c

untuk deret aritmatika berlaku
U2-U1 = U3- U2
(2k+ 16) – (3k+12) = (44-k) – ( 2k+16)
2k – 3k + 16 – 12 = -k -2k + 44 – 16
– k + 4 = -3k + 28
-k + 3k = 28 – 4
2k = 24
k = 12

jadi U1 = 3k + 12
            = 3(12) + 12
           = 36 + 12
           = 48
U2 = 2k + 16
     = 2(12) +16
     = 24 + 16
     = 40
U3 = 44- k
     =  44- 12
     = 32
b = 48-40 = -8

un = a + (n-1)b
     = 48+ (n-1)(-8)
     = 48 – 8n +8
     = 56- 8n
     = 8 ( 7 – n)
jawaban C