A right square pyramid, vertex O, stands on a square base ABCD. The height is 15cm and base length is 10cm. Find:

a. the length of the slant edge : I got that: 5 root 11.

b. the inclination of a slant edge to the base : 64.76 degrees

c. the inclination of a sloping face to the base : 71.57 degrees

d. the madnitude of the angle between two adjacent sloping faces : I have no idea about this one! Please help it is the angle between the faces?! I can't picture it.