11, 18, 25, 32, ..., a8
we notice that we have an A.P where a1= 11 and r= 7
a1= 11
a2= 11+7 = 18
a3= 11+7*2 = 25
a4 = 11+ 7*3= 32
a5= 11 + 7*4= 39
a6 = 11+ 7*5 = 46
a7 = 11+ 7*6 = 53
a8 = 11 + 7*7 = 60
Then the sum is:
S = 11 + 18 + 25 + 32 + 39 + 46 + 53 + 60 = 284
Then the sum = 284