24 : 12

Explanation:
Each pair of numbers is related in some way.

For the first pair, 2 • 6, the relationship is multiplication, so the result is 12.

For the second pair, 16 : 2, the relationship is division, so the result is 8.

For the third pair, 18 : 9, the relationship is division, so the result is 2.

For the fourth pair, 12 : 2, the relationship is division, so the result is 6.

For the fifth pair, 3 • 14, the relationship is multiplication, so the result is 42.

For the sixth pair, 2 • 3, the relationship is multiplication, so the result is 6.

For the final pair, 9 • 2, the relationship is multiplication, so the result is 18.

Putting all the results together, we get 24 : 12.