[填空题]
Two stones are thrown g h d2dw2lfy8 3oky2v(vertis1a tzbn ow) q(6cdj;qz9,u4 qcally up at the same time. The first stone is thrown with an initial velocity of 11.0 m/s froq)zcuqa4sq 6 z9, w1njb;(dto m a 12th-floor balcony of a building and hits the ground after 4.5 s. With what initial velocity should the second stone be thrown from a $4^{th}$-floor balcony so that it hits the ground at the same time as the first stone? Make simple assumptions, like equal-height floors. m/s
