Thank you so much for helping me out with this problem

if I have a joint distribution

fXY (x,y) =24(xy) x > 0; y > 0; x + y < 1

0 otherwise

how can I calculate the FX,Y (x, y)?

∫∫24xydydx

I can't figure out the limit for this calculation.

and how can I plot this in R

Thank you