[填空题]
Two stones are thrown q7bnb ck d.7ll91 hy cz*hxyv57l7ij 1vertically up at the same ti5eiu2ub8. 4fktq5mph me. The first stone is thrown wih5 muetf4pb. 5ku2 iq8th an initial velocity of 11.0 m/s from 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
