There is no solution to the equation.
The x is cancelled out.
See attachment file below.
Hope it helped!
With
in quadrant 3, we should expect both
and
to be negative, so that
is positive. The corresponding reciprocal expressions
will have the same sign.

Recall that
, which means


Also recall that
, so


Only the first two options are correct.
2x+3y=60 solve for x...
x=(60-3y)/2
p=xy^3, using x from above:
p=y^3(60-3y)/2
p=(60y^3-3y^4)/2
dp/dy=(180y^2-12y^3)/2
dp/dy=90y^2-6y^2
dp/dy=0 when:
90y^2-6y^3=0
6y^2(15-y)=0, we know y>0 so
y=15, since x=(60-3y)/2
x=7.5
(We solved it this way because otherwise you get quartic equations and cubic derivatives, yuck :P)