To solve this problem, you can split the shape to make it simpler.
(See the photo attached to see how it’s divided)
After doing that, you end up with a rectangle that’s 5 cm by X amount of cm.
And another rectangle that is 4 cm by 13 cm
Then you need to find the unknown.
Looking at the shape, you can see that the side length is 11 cm. Looking at the lower rectangle, you can see side length (farthest measurement to the right) of the lower rectangle is 4 cm. the lower rectangles 4cm side length is part of the 11cm side length on the whole shape. So to find the answer, you must subtract the 4cm side length from the 11cm side length.
To find the unknown you take 11 cm and subtract 4cm.
So now we have a smaller rectangle that is 7cm by 5cm, so the unknown = 7cm.