lalalaudh

t = t2 - t1 = d/v2 - d/v1 " p. m4 o% k# o
, J* O4 |8 {0 B" R& a
so answer is :
1 M5 Y: C" A' H8 S2 P& y" N. stvb now,tvbnow,bttvb
8 P% Z( ^, `6 J2 j: ^! L4 x3 {* yTVBNOW 含有熱門話題，最新最快電視，軟體，遊戲，電影，動漫及日常生活及興趣交流等資訊。d = t * v1 * v2 / (v1-v2)