find the partial sum

100

∑ 6n

n=10

ok this is what i did but i didnt get the same answer as the book can someone tell me what i did wrong please?

100

∑ 6n

n=10

60+66+72+78+...

a1=60 d=66-60--> d=6

c=a1-d --> c=60-6 --> c= 54

an= dn+c --> an= 6n+54 --> a100=6(100)+54 --> a100= 654

Sn=n/2(a1+an) --> Sn=100/2(60+654) --> Sn= 35700 which is the wrong answer......aarrrrrrrrrrrrrrrrhhhhh

i looked in the back of the book and the correct answer is 30,030. what did i do wrong?