2009 AMC 10B Problem 4

A rectangular yard contains two flower beds in the shape of congruent isosceles right triangles. The remainder of the yard has a trapezoidal shape, as shown. The parallel sides of the trapezoid have lengths $15$ and $25$ meters. What fraction of the yard is occupied by the flower beds?

$\text{(A) } \frac {1}{8} \qquad \text{(B) } \frac {1}{6} \qquad \text{(C) } \frac {1}{5} \qquad \text{(D) } \frac {1}{4} \qquad \text{(E) } \frac {1}{3}$