Let's perform the synthetic division
#color(white)(aaaa)##3##color(white)(aaaaa)##|##color(white)(aaaa)##1##color(white)(aaaaaa)##-1##color(white)(aaaaaa)##-14##color(white)(aaaaaaa)##25#
#color(white)(aaaaaaaaaaaa)#_________
#color(white)(aaaa)##color(white)(aaaaaaa)##|##color(white)(aaaa)##color(white)(aaaaaaaa)##3##color(white)(aaaaaaaa)##6##color(white)(aaaaa)##-24#
#color(white)(aaaaaaaaaaaa)#________
#color(white)(aaaa)##color(white)(aaaaaaa)##|##color(white)(aaaa)##1##color(white)(aaaaaaa)##2##color(white)(aaaaaaa)##-8##color(white)(aaaaaaa)##color(red)(1)#
#(x^3-x^2-14x+25)/(x-3)=(x^2+2x-8)+1/(x-3)#
The remainder is #=1# and the quotient is #=x^2+2x-8#