(leave the 15 alone for the duration of the sum)
= 5*675 - 5*3*210 - 210   ------------------------------ time's out bracket 
 =5*675 -210(5*3 +1)   ---------------------------- took out common "-210" out of last  
                                                                        two terms'
= 5*675 -210(15+1)
= 5*675 -210(16)
=5*675 -210*16