Select the number that best completes the analogy: 34 : 12 :: 56 : ?

The relation is a two-digit number : the product of its two digits. In 34 the digits give $3\times 4=12$, so 56 gives $5\times 6=30$. The trap is 11, which is the sum of the digits (5 + 6) — a weaker rule that happens to look reasonable until it is tested on the first pair, where 3 + 4 = 7, not 12.