Maximize[20000 x+12000 y,{x+y<=500,15000 x+10000 y<=500000,x<=3/10 (x+y),y>=1/4 (x+y),x>=0,y>=0},{x,y}]

Maximize[20000 x+12000 y,{x+y<=500,15000 x+10000 y<=500000,x<=3/10 (x+y),x>=0,y>=0},{x,y}]