Let's perform the synthetic division
color(white)(aaaa)-3|color(white)(aaaa)1color(white)(aaaa)3color(white)(aaaaaa)-5color(white)(aaaaa)0color(white)(aaaaaa)9
color(white)(aaaaaaa)#|color(white)(aaaa)##color(white)(aaa)-3#color(white)(aaaaaaa)0color(white)(aaaaa)15color(white)(aaaa)-45
color(white)(aaaaaaaaa)_________________________________________________________##
color(white)(aaaaaaa)#|color(white)(aaaa)#1color(white)(aaaa)0color(white)(aaaaaa)-5color(white)(aaaa)15color(white)(aaaa)color(red)(-36)
The remainder is =-37 and the quotient is x^3-5x+15
(x^4+3x^3-5x^2+0x+9)/(x+3)=(x^3-5x+15)-36/(x+3)