If you split the rectangle, you are left with two triangles. One side is 15, and the other is 12. If you plug this into the pathagorean thereom, it wold look like 15(squared) + 12(squared) = x (squared)
15 squared is 225. 12 squared is 144. 225 plus 144 = 369. This means that the hypotenuse is the square root of 369.
The square root of 369 is 19.2094..... or when rounded, 19.21.
