Use the graphical method to find all optimal solutions

for the following model:

Maximize Z $=500$x$1+300$x$2,$

subject to

$15$x$1+5$x$2<=300$

$10$x$1+6$x$2<=240$

$8$x$1+12$x$2<=450$

and

x$1>=0,$ x$2>=0.$