question 6 i finally figured it out with a little help from bjorn and louis

Ok since it is the end of the day,i finally solved it here it is.
^_^
6)dy/dx(ax+b/x^2)=a-2b/x^3
sub x=3,y=5 into this equation,it will give you 27a+b=45-eqn1
dy/dx=0,sub x=3,to give u equation 27a-2b=0-eqn2
Solve the equations simultaniousely to give you
A=10/9 and B=15.