Let's perform the synthetic division
#color(white)(aaaa)##3##color(white)(aaaaa)##|##color(white)(aaaa)##1##color(white)(aaaaaa)##-10##color(white)(aaaaaa)##15##color(white)(aaaaa)##20#
#color(white)(aaaaaaaaaaaa)#_________
#color(white)(aaaa)##color(white)(aaaaaaa)##|##color(white)(aaaa)##color(white)(aaaaaaaa)##3##color(white)(aaaaa)##-21##color(white)(aaaa)##-18#
#color(white)(aaaaaaaaaaaa)#________
#color(white)(aaaa)##color(white)(aaaaaaa)##|##color(white)(aaaa)##1##color(white)(aaaaaa)##-7##color(white)(aaaaa)##-6##color(white)(aaaaaa)##color(red)(2)#
The remainder is #=2# and the quotient is #=v^2-7v-6#
#(v^3-10v^2+15v+20)/(v-3)=v^2-7v-6+2/(v-3)#