To solve this problem you must apply the proccedure shown below:
1. She has a total of 50 DVDs of 90 minutes each one of them. The cost of each DVD was 11€.
2. Therefore, to calculate the total cost of the collection, you must multiply the cost of each DVD by the total number of them:
€
3. To calculate the total minutes of the collection, you must multiply 90 minutes by the total number of DVDs:

Therefore, the answer is: 550€ and 4500 minutes.
We know that
The Euler's formula state that, the number of vertices, minus the number of edges, plus the number of faces, is equal to two
V - E + F = 2
clear F
F=2-V+E
in this problem
V=8
E=14
F=?
so
F=2-8+14
F=8
the answer is8 faces
You need to know atleast 2 of three sides from a triangle, or 1 side and 1 angle of a triangle. Then you can use trigonometry to find the angle needed.