Three sides to a triangle, let's call them a, b and c.
The perimeter is a+b+c
a=2ft=24in
b=18in
c=?
Pythagoras' Theorem is a²+b²=c²
a²+b²=c²
24²+18²=c²
576+324=c²
900=c²
√900=c
30=c
a=24in
b=18in
c=30in
perimeter=a+b+c
perimeter=24+18+30
perimeter=42+32
perimeter=72
72in=6ft