solve 3 questions on perimeter & area of triangles

2. we can find third side by using pythogoras theorem.

that will be 4.

let the sides be 3k,4k,5k

so 3k+4k+5k = 36  ==>  k= 3

so sides of the triangle will be 9,12,15

area of this triangle will be 1/2(9)(12) = 54