Answer:
-$15
Step-by-step explanation:
To find the average yearly change, divide -120 by 8, since it has decreased by $120 over 8 years.
-120/8
= -15
So, the average yearly change in the value of the card is -$15
Answer:
B
Step-by-step explanation:
10 + (-42)
10 - 42
-32
Answer: 
Step-by-step explanation:

Divide by 23

Extract the square root.

Answer:
A book is worth $1 and a DVD is worth $12.
Step-by-step explanation:
The equations (2 unknowns and two equations, d is for a DVD and b is for a book):
For David: 3d+4b=40
For Anna: d+6b=18
Now multiply the second equation with -3 and add to the first equation:
3d+4b=40
−3d−18b=−54
Combined equation: −14b=−14 and b=1 (means that each book is worth $1).
Now for DVD price, use the second equation:
d=18−6 or d=12 (means that each DVD is worth $12).
A book is worth $1 and a DVD is worth $12.