Let's convert the problem into Arithmetic progression:
It would be: 5, 9, 13, ....
Here, a = 5, d = 9 - 5 = 4
We know, S(n) = n/2 [ 2a + (n-1)d ]
Substitute the known values,
434 = n/2 [ 2(5) + (n - 1)4 ]
434 * 2 = n [ 10 + 4n - 4 ]
868 = 10n + 4n² - 4n
= 4n² + 6n - 868 = 0
d = b² - 4ac
d = 6² - 4(4)(-868)
d = 36+13888
d = 13924
Now, roots = -b +- √d / 2a
= (-6 + √13924) / 2(4) OR (-6 - √13924) / 2(4)
= (-6 + 118) / 8 OR (-6 - 118) / 8
= 112/8 OR -124/8
= 14 OR -15.5
As number of sticks can't be in negative/decimal or fraction form, -15.5 would be fully rejected.
In short, Your Answer would be 14 [ Remaining root ]
Hope this helps!