Side length of a square in a squared rectangle I have a squared rectangle where I want to find the side length of a sub-square (for the record, consult the omniscient Google).

Here's what I've already done.
$$14 + 4 + x = \mathrm{height}.$$
The teeny square has a side length of 1.
If the square to the right of the tiny square has side length $a$, $$x = 9 + a - 1.$$ This problem would be a lot easier if the rectangle were a square (if you think it is, prove it), but I'm not sure what to do now.

Follow these steps:
left middle square is 10, because 14-4
tiny square is 1, because 10-9
square below tiny is 8, because 9-1
square to the right of tiny is 7, because 8-1
x is 15, 7+8
The answer is
E) 15 
