Complete Question:
The complete question is shown on the first uploaded image  
Answer:
a) The graph of  f(y) versus y. is shown on the second uploaded image
b) The critical point is at y = 0  and the solution is asymptotically unstable.
c)The phase line is shown on the third uploaded image 
d) The sketch for the several graphs of solution in the ty-plane  is shown on the fourth uploaded image 
Step-by-step explanation:
Step One: Sketch The Graph of  f(y) versus y
Looking at the given differential equation 
         for -∞ <
 for -∞ <  < ∞
 < ∞
  We can say let  = f(y) =
 = f(y) =
Now the dependent value is f(y) and the independent value is y so to sketch is graph we can assume a scale in this case i cm on the graph is equal to 2 unit for both f(y) and y and the match the coordinates and after that join the point to form the graph as shown on the uploaded image.
Step Two : Determine the critical point 
    To fin the critical point we have to set    = 0
 = 0
        This means  = 0
 = 0
                           For this to be possible  = 1
 = 1
                           which means that   =
 = 
                           which implies that y = 0
 Hence the critical point occurs at y = 0 
meaning that the equilibrium solution is y = 0
As t → ∞, our curve is going to move away from y = 0  hence it is asymptotically unstable.
Step Three : Draw the Phase lines 
A phase line can be defined as an image that shows or represents the way an ODE(ordinary differential equation ) that does not explicitly depend on the independent variable behaves in a single variable. To draw this phase line , draw the y-axis as a vertical line and mark on it the equilibrium, i.e. where  f(y) = 0. 
In each of the intervals bounded  by the equilibrium draw an upward
pointing arrow if f(y) > 0 and a downward pointing arrow if f(y) < 0. 
       This phase line would solely depend on y does not matter what t is
On the positive x axis it would get steeper very quickly as you move up (looking at the part A graph).
For  below the x-axis which stable (looking at the part a graph) we are still going to have negative slope but they are going to be close to 0 and they would take a little bit longer to get steeper   
Step Four : Draw a Solution Curve 
 A solution curve is a curve that shows the solution of a DE (deferential equation) 
Here the solution curve would be drawn on the ty-plane 
So the t-axis(x-axis) is its the equilibrium  that is it is the solution
If we are above the x-axis it is going to increase faster and if we are below it is going to decrease but it would be slower (looking at part A graph)