You have the right idea and you are close to the correct answer. However that's not what your teacher is looking for in terms of steps.
The starting inequality is

She starts off selling 8 buckets. Then she sells b more to get a total of b+8
This total must be 20 or larger which is why I set b+8 greater than or equal to 20
Solve for b by subtracting 8 from both sides



So she needs to sell at least 12 more buckets to reach her goal
If you graphed this on a number line, then you would draw a closed circle at 12. Then shade to the right of the close circle.
A)
2, 4, 6, 8, *10
The fifth row contains 10 cans.
----------------------------------------------------
b)
2+4+6+8+10+12+14+16+18+20=110
-----------------------------------------------------
c)
2*Row=Number Of Cans
When Row=1, Number Of Cans=2.
When Row=5, Number Of Cans=10.
When Row=10, Number Of Cans=20.
Answer:
the measure of supplementary angles must add up to 180
Step-by-step explanation:
complementary angles add up to 90°
angles on a straight line are supplementary angles which add up to 180°
the answer to the first question would be 
the answer to the second question will be 