if we look on one side, we already have one measurement. 4 cm. ok, that's the measurement on that side. look to the left now. that other side is also the same length, so we take that number and multiply it be 2 to get
Wait! we're not done yet. look at the top. do you see the 3? well that's the width for the top of the rectangle. the bottom must be the same to right? so we get
add both equations and you get
The answer is 14cm! Don't forget to label. ;)