Need help figuring out a pattern question

Question

my cousin asked for help on this math problem and the answer is apparently 6 but i can't find a coherent pattern that fits all of the triangles. I included an image of the question.

Answer 1

The missing no is 6. Sum of numbers in each horizontal layer is 36.

Answer 2

The number is $n=66$. The sum of all alternating sums of the rows should equal zero. So we need $$ 36+(30-n)-8+8=0, $$ which says that $n=66$. For example, the last row has alternating sum $$4-7+5-4+5-3+8=8$$