Star Mosaic - 5

Since the star is composed of 6 equal parts it is easier to just focus on one part and then multiply by 6. We can see that each layer adds 4 new triangles and the first layer has 2.

$f(n) = 2 + 4*(n-1)$

$f(5) = 2 + 4*4 = 18$

To get the whole star we just multiply our answer by 6.

$18 * 6 = \boxed{108}$

12(2n-1) = 12(2 * 5(th layer) - 1) = 12 * 9 =108(Ans.)

Each triangle adds up 24 therefore just add 24 :

1st layer = 12

2nd layer = 12 + 24 = 36

3rd layer = 36 + 24 = 60

4th layer = 60 + 24 = 84

5th layer = 84 + 24 = $\boxed{108}$