Nice ratio problem #1

ABC is a right triangle in B such that [AB] $= 3$ and [BC] $= 5$ . BFDE is a square

What is the area ratio of ​BFDE to ABC ? This ratio can be written as $\frac{a}{b}$ where $a$ and $b$ are coprime positives integers. Find $a + b$ .

Note that the diagram above is not at the scale .