Differentation...help please :)

Hi , i have this question i have answered the first two parts , but im not sure if there right and im also unsure about the last parts. Thank you for your help.

A piece of wire 16cm long is cut into two pieces . One piece is 8x cm long and is bent to form a rectangle measuring 3x cm by x cm long. the other piece is bent to form a square.

i) find in terms of x,

a) the length of a side of the square, i got the width to be 2cm and the length 4cm.

b)the area of the square , i got to be 4cm^2.

ii) Show that the combined area of the rectangle and the square is Acm^2, where A=7cm^2-16x+16. Not sure how to do this at all, not sure if i got the ones i worked out right :S

iii) lastly i need to find the value of x for which A has its mimimum value, and also find this minimum value for A.

Thank you for your help :)