tolong dong kak pakai cara plis cepet ya tolong bantuannya

Nomor brp kak 7,8?
..........

7. A = 3
B=u2-u1
=8-3=5
u20 = A+19*B
=3+19*5
=3+95 =98 (B)
8.U6=a*R^5=384
U1 =a. =12
=r^5. =32
=R = 2
u6=A*R^5=384
=a * 32 =384
=a =12
s6=a (r^6-1) / r-1 =
=12 (63)/2-1
=756 cm (B)
semoga bermanfaat dan membantu