From the setup of the problem, the "length of the top of the bookcase, measured along the attic ceiling" will be the hypotenuse of a right triangle, the length "AB". We have both the angle between AB and AC and the length of AC (3.24 meters), so we can use trigonometric identities.
The cosine of the 40 degree angle between AB and AC is equivalent to the length of AC divided by the length of AB. Equivalently, we have:

where "h", the hypotenuse, is the length we want. Rearranging the formula to solve for h we have that

which is 4.2295... meters. Converting to centimeters (multiplying by 100) we have that h = 422.95... centimeters, or if we round the value, h = 423 centimeters.
Answer:
wrong the answer is 63.1
Step-by-step explanation:
The answer: <span>13.634
Don't believe me? Check with a(n) calculator!</span>
If 2 of 12 eggs are cracked, then 10 are not cracked.
SO
10/12=5/6=about 0.83
0.83 of total eggs not cracked is also equivalent to 83 percent as asked in the problem :)
Looks like the system is

We can eliminate
by taking




so that
, and



Substitute
into this last equation and solve for
:




Then



Plug these values into any one of the original equation to solve for
:




Hence the solution is x = 4, y = -3, and z = 2.