Linear problem, need a little help. :)

Ok i have this homework set for my A level H.W and i need a little help on finding the objctive function.

question =

100x + 150y

4x + 4y </= 600

x + 6y </= 480

x,y >/= 0

Note: </= is less than or equal to for this example :)

I'm stuck on finding this part of the question

100x + 150y

i've put in a number which both goes into

100x + 150y = 300

which leaves me with x=3, y=2

and when i plot that onto a graph it doesn't fit well because all the other answers are much larger.

Any help would be great! :)

thanks