It could be 8 since 8x18= 144 and 144 divided by 2 is 72
TO find perimeter you add all sides. But to find the totaly of each side, you will divide. So a triangle has 3 sides, so you divide 45 by 3 to get the sides length of:
15 cm each
~hope this helped :)
The answer you're looking for my good lad is C