So the speed of B is 4/4= 1 unit/second.

(2)4-(-8)= 12,

(12-6)/(2-1) = 6,6 seconds, with a difference of 6 unit lengths.

(3) Let the speed of C be V units/second, 1

CB=4+(v- 1)t，CA=8+(2-v)t，

From CB: ca =1:2,8+(2v-2) t = 8+(2v) t,

(3v-4)t=0，t & gt0,

∴v=4/3.

T=7.5 seconds when C stays at-10, and the position of point B is 4-7.5* 1=-3.5.