To find the area of an obtuse triangle you have to multiply the base of the triangle by the vertical height and divide the result by 2 following the formula:

The base of the triangle is b= 7 miles and the height is h= 8 miles, using these lengths calculate the area as follows:

The area of the triangle is 28 square miles.
Ok this is a bit complicated.
Total: 114 days
114 divided by 3 equals 38
38 times 2 equals 76
76 books, I think.
C=2*pi*r
2*3.141592654*2.5
Answer: 15.7 cm