Answer:54cm^2

According to the herons formula

area of a triangle=√s(s-a)(s-b)(s-c). [where s=(a+b+c)/2 and a,b,c are the sides]

9+12+15=36cm

s=36/2

s=18cm

area=√s(s-a)(s-b)(s-c)

=√18*(18-9)*(18-12)*(18-15)

=√2916

=54cm^2

Answer:

√s(s-a)(s-b)(s-c) Where S= A+B+C/2

9+12+15/2 = 18

So =√18(18-9)(18-12)(18-15)

=√18(9)(6)(3)

=√18(9) ×18 = 18√9 = 18×3 = 54

Answer = Area Of A Traingle Is 54