Respuesta :

a)
Because it is a square
Area =a²
324 = a²
a=√324= 18
a=18 cm

b)
Side of inner border = 18-2-2(from up and down  for example)
Side of inner border = 18-2-2= 18-2*2= 14 cm

c)
Area of inner square=14²=196 cm²