Answer:
<em>D. Obtuse</em>
Step-by-step explanation:
For this case we can propose an equation that will allow us to find the price of one of the books knowing the price of the other.
x: Let the variable that represents the price of the book with a green sticker
y: Let the variable that represents the price of the book with a yellow sticker
According to the statement we have:


Finally, we can substitute the price of one of the books and clear the value of the other as the case may be.
Answer:

Both angles are complementary and add up to 90 degrees. If you do that in an equation it should be like this:
2x + 14 + x + 7 = 90
Simplify:
3x + 21 = 90
3x = 69
X = 23
Now just plug that into angle CBD and you get:
2(23) + 14 = y
46 + 14 = y
60 = y
Angle CBD is 60 degrees
Sin(angle) = opposite leg / hypotenuse
Sin(45) = Opposite leg / 28
Opposite Leg = 28 * Sin(45)
Opposite Leg = 14 SQRT(2) = 19.8