Select the number that best completes the analogy: 8 : 36 :: 11 : ?

The relation is $n$ : the total of all whole numbers from 1 up to $n$, which is $n\times (n+1)÷2$. For 8 that total is $8\times 9÷2=36$, so for 11 it is $11\times 12÷2=66$. The distractors each stop one step away: 55 is the total up to 10, 78 the total up to 12 and 121 is simply 11 squared.