tolong bantu jawab aku gak ngerti:'(

a) a = 3
    U8 = a + 7b
    24 = 3 + 7b
    7b = 24 - 3
      b = 21/7
      b = 3

b) Un = a + (n - 1)b
          = 3 + (n - 1) 3
          = 3 + 3n - 3
          = 3n

c) U10 = 3 + (9)3
           = 30
    Sn = n/2 (a + Un)
    S10 = 10/2 (3 + 30)
           = 5 (33)
           = 165

a=U1=suku pertama=3
U8=24

b..?
deret..?
S10...?

Sn=n/2(a+Un)
S8=8/2(3+24)
=4(27)
=108

Sn=n/2(2a+(n-1)b)
S8=8/2(2.3+(8-1)b)
108=4(6+7b)
108=24+28b
108-24=28b
84=28b
84/28=b
3=b
beda =3

deret
U1+U2+U3+U4+U5...
3+6+9+12+15

S10=10/2(2.3+(10-1)3)
=5(6+27)
=5(33)
=165