Question 23401
I'll set up the equations and let you do the solving.
Let number of library be "a"
Let number of telephone be "b"
Let number of textbook be "c"
Then:
  a + b + c = 36
  c + b = 3a
  a + b = 2c
Rearrange to get :
 a + b + c = 36
 3a -b -c  = 0
 a + b -2c = 0

Answer is a=9, b=15, 12

Cheers,
Stan H.