(1)S=V0t+1/2at^2,36=18×3+4.5a,a=-4m/s^2!Vt=V0+at,Vt=18-12=6m/s!(2)△x=aT^2
,36=9a,a=-4m/s^2,V同上!不好意思第三种还没想到!