Answer: 27 leaves

Formula for finding this is: \(\displaystyle (number of vertices+1)/2\)

...look at a smaller examples/full binary trees to see that this works:

Every full binary tree with 7 vertices has 4 leaves.

\(\displaystyle (7+1)/2 = 8/2 = 4\)

Every full binary tree with 15 vertices has 8 leaves.

\(\displaystyle (15+1)/2 = 16/2 = 8\)