then you applied it incorrectly
for a right triangle with legs legnth a and b and hypotonuse c,
a^2+b^2=c^2
hypotonuse=longest side or side oposite right angle
so we see that
hypotnuse=c=unknown
legs are legnth a and b or12 and 9
plug in
a=12
b=9
c=c
a^2+b^2=c^2
12^2+9^2=c^2
144+81=c^2
125=c^2
sqrt both sides
15=c
the legnth of the hypotnuse=15
to find the perimiter, you add all sides up
a+b+c=
12+9+15=
36
answer is 36 inches
B is answer
