Ok so area=162 since the triangles sides were cut out of a square, base=height area=1/2bh=162 b=h area=1/2b^2=162 times 2 both sides b^2=324 sqrt both sides b=18=h the legnth of one side is 18cm see diagram
another way, is total aera of square=areas of both triangles=162+162=324 remember area of square=side^2 so 324=side^2 sqrt both sides 18=side