Rearrange the polynomials in decreasing powers of #x#
Let's do the long division
#color(white)(aaaa)##x^4-5x^3+x^2-5x##color(white)(aaaa)##∣##x+5#
#color(white)(aaaa)##x^4+5x^3##color(white)(aaaaaaaaaaaaa)##∣##x^3-10x^2+51x-260#
#color(white)(aaaa)##0-10x^3+x^2#
#color(white)(aaaaaa)##-10x^3-50x^2#
#color(white)(aaaaaaaaaa)##0+51x^2-5x#
#color(white)(aaaaaaaaaaaa)##+51x^2+255x#
#color(white)(aaaaaaaaaaaaaaaa)##0-260x#
#color(white)(aaaaaaaaaaaaaaaaaa)##-260x-1300#
#color(white)(aaaaaaaaaaaaaaaaaaaaaaa)##0+1300#
You can use the remainder theorem
#f(x)=x^4-5x^3+x^2-5x#
#f(-5)=625+625+25+25=1300#