A device runs until either of two components X and Y fails, at which point the device stops running. The joint density function of the lifetimes of the two components, both measured in hours, is

$\displaystyle f(x, y) = \frac{x + y}{27}$ for 0 < x < 3 and 0 < y < 3.

how can you calculate the probability that the device fails during its first half hour of operation?

thank you for your help