Tim has preferences represented by the utility function U(x,y)=min(6x+y,x+2y) ,if x is on the horizontal axis and y is on the vertical axis ,what is the slope of his indifference curve at the point (8,9)

答案是啥，-2分之1么？但老师给的怎么是-6分之1

另外还有一道题目， moll's unility function is u(x.y)=y+4x*0.5次方，she has 25 units of x and 12units of y ,if her consumption of x is reduced to 0,how many units og y would she need in order to be exactly as well off as before ???