Question 936434
In General, # is not have any significance pertaining to maths
But in this problem, # is defined as a condition. we have to use those conditions to solve the problem
       given conditions :   a8b=a-3b    a#b=2a+3b
  4*3  = 4-3(3)  ( here a=4 , b=3)
        = 4-9
        =-5
(4*3)#5  = (-5)#5 
  (-5)#5  = 2(-5)+3(5)   ( here a=-5  b= 5)
          =-10+15
        = 5
 Result :(4*3)#5 =5