Tolong bantu jawab yaa

201+204+207+........+297
a=201
b=3
un=a+(n-1)b
297=201+(n-1)3
297=201+3n-3
297=3n+198
3n=297-198
3n=99
n=33
Sn=n/2(a+un)
=33/2(201+297)
=33/2×498
=249×33
=8217