3. Find x. Please help and explain

What is the approximate total length of iron edging needed to create the square frame and the two diagonals?

If f(x)=-x^2+6x-1 and g(x)=3x^2-4x-1,find(f+g)(x)

In trapezoid abcd, ac is a diagonal and ∠abc≅∠acd. find ac if the lengths of the bases bc and ad are 12m and 27m respectively.