To solve, we have to look for a pattern.
When you see pyramids like these, they usually tell you to add/multiply the two numbers to get a third number that goes on top. Here, we can see 3 and 4 on the bottom left hand corner. The third number on top of both 3 and 4 is 7. 3 + 4 = 7. Let's check 4 and 5, the middle two numbers. 4 + 5 = 9, and that number is on top of 4 and 5. Therefore, we can confirm that this is an addition pyramid.
Since 7 + 9 is 16 and 9 + 8 is 17, all we need to do in order to get the final number is to add 16 to 17.