Condtions : I assumed that the first term of the dividend is #=3x^3#
Let's perform the synthetic division
#color(white)(aa)##-3##color(white)(aaaaaa)##|##color(white)(aaa)##3##color(white)(aaaaaaaa)##14##color(white)(aaaaaaa)##20##color(white)(aaaaaa)##29#
#color(white)(aaaaaaaaaaaa)##------------#
#color(white)(aaaa)##color(white)(aaaaaaa)##|##color(white)(aaaa)##color(white)(aaaaaaa)##-9##color(white)(aaaaa)##-15##color(white)(aaaaa)##-15#
#color(white)(aaaaaaaaaaaa)##------------#
#color(white)(aaaa)##color(white)(aaaaaaa)##|##color(white)(aaa)##3##color(white)(aaaaaaaaa)##5##color(white)(aaaaaaa)##5##color(white)(aaaaaaa)##color(red)(14)#
The remainder is #color(red)(14)# and the quotient is #=3x^2+5x+5#
#(3x^3+14x^2+20x+29)/(x+3)=3x^2+5x+5+14/(x+3)#