Your graph is correct.
You start with point (0, 40). On day 0, you have 40 T-shirts.
Each day that passes, you have 5 shirts fewer. (1, 35) means on day 1, you have 35 shirts left. Each day that passes, there are 5 fewer shirts. On the 8th day, there are no shirts left. That is point (8, 0).
Good job!
Answer:
You can get it by doing this
Step-by-step explanation:
The Probability
Substitute this into the parabolic equation,
We're told the line 
intersects 
twice, which means the quadratic above has two distinct real solutions. Its discriminant must then be positive, so we know
We can tell from the quadratic equation that has its vertex at the point (3, 6). Also, note that
and
so the furthest to the right that extends is the point (5, 2). The line passes through this point for 
. For any value of 
, the line passes through either only once, or not at all.
So 
; in set notation,
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