[填空题]
A baseball is seen tja pi)(1zj snw5+s88zgn ml k2o pa5i((x iwol,b 9 3zl+k,ghxjj lss upward by someone on the 9th floor (28 m above the street) with a verticaw, +l,xllij bg hz9(5(3ijx okl speed of $20 \; m/s$. If the ball was thrown from the street, (a) what was its initial speed? $m/s$ (b) what maximum altitude does it reach? $m$ (c) how many seconds ago was the baseball thown from the street? $s$ (c) In how many seconds will it reach the street again? $s$
