[填空题]
A baseball is seen to pass upaov a dm5.j-uk,rnid y+2,l,uward by someone on the 9th floor (28 m above -w wkiy1 ;wrdjmy8cu voc3d64*aymq d(.h 00q the street) with a vertical speed of dw*qrujh dik80mqmy0 13; c(wd4oac.- wy6y v $20 \; m/s$. 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? $s$
