Graphical Method can be used.
On solving all the constraints, the peaks of the common area are:
A(0,0), B(0,600), C(1500,0), D(1000,500)
z is maximum on all the points of the constraint x1+x2<=1500 (as slope of z is same as the constraint)
Now lets try to eliminate the options
opt 1 and 2 can be eliminated as they are violating 3rd constraint
opt 4 can be eliminated as it is violating 1st constraint
Hence, opt 3 is the answer