Answer: After 7 years the number of birds of species A and B are same. and the number of birds during that year will be 140.
Step-by-step explanation:
Given: Sharon is conducting research on two species of birds at a bird sanctuary.
The number of birds of species A is represented by the equation below,where S represents the number of birds, x years after beginning her research.

The number of birds of species B is represented by the equation below,where S represents the number of birds, x years after beginning her research.

To plot the above function, first find points by which they are passing.
For species A, At x=0 , 
At x=2 , 
Similarly find more points and plot curve on graph.
For species A, At x=0 , 
At x=2 , 
Plot a line with the help of these two points.
Now, from the graph the intersection of curve (for A) and line (for B) is at (7,140) which tells that After 7 years the number of birds of species A and B are same. and the number of birds during that year will be 140.
A=a+b+c+d/4
subtract a from both sides
0=b+c+d/4
Subtract b from both sides
-b=c+d/4
Finally subtract d/4 from both sides
c=-d/4-b
The NFL started August 20, 1920