The future lifetimes (in months) of two components of a machine have the following joint density function:

$\displaystyle f(x,y)=\left\{\begin{array}{lr}(6/125,000)(50-x-y)&0 < x < 50-y < 50\\0&otherwise\end{array}\right.$

What is the probability that both components are still functioning 15 months from now? thanks for your help