Answer:
AB = 27cm
Explanation:
Since the two rectangles are similar, we can write a proportion
(fraction = fraction)
to solve this problem. "Similar" means that the rectangles are exactly the same shape, but just different sizes. However, the ratios of the sides are equal.
You can compare like things, such as:
comparing corresponding sides: side/side or bottom/bottom
OR you could write a ratio comparing two sides of the small rectangle, such as: side/bottom and set that equal to the same ratio made from the big rectangle.
The big hint is to re-draw the picture where you draw the small shape and separately draw the big shape. Then you can see what measures correspond.
see image.
Write a proportion and solve by cross-multiplying.
see image.