Question 750039
We use Heron's formula

{{{
A=sqrt(s(s-a)(s-b)(s-c))
}}}



where 



{{{
s=(a+b+c)/2
}}}

Now a=15, b=20, c=25




{{{
s=(a+b+c)/2=(15+20+25)/2=30
}}}




{{{
A=sqrt(s(s-a)(s-b)(s-c))=sqrt(30(30-15)(30-20)(30-25))=150
}}}




:)