Answer:
S6=275548
Step-by-step explanation:
a=28 r=
[tex] \frac{t2 }{t1} [/tex]
r=
[tex] \frac{84}{28} [/tex]
S9=
[tex] \frac{28 - 28(3) {}^{9} }{1 - 3} [/tex]
S9=275547
