can you help me with this analysis question?

[jenerator]

paula does stunts for televevision shows. fro one stunt she has to jump form the top of a tall building. Her height (y meters) above the ground at time is t seconds from when she jump is given by y=21+t-5t^2.

a) by solving y=0, find when paula reaches the ground correct to two decimal places.
b) the formula y can be written in the form y=-5(t+h) +k. exaplin why h= 0.01 and k= 21.05
c) a large air mattress is used to to cushion paulas landing. If matress in 2 m thick, find when, to the nearest one hundreth of a second, paula first comes into contact with the mattress
this is yr 11 stuff

[b^3]

are you sure h=0.01, because its works for h=-0.1, and isn't the form y=-5(x+h)^2+k ?
anyway here it is if they above were typos
a) y=0 substitue and use quadratic formula to solve

so a=-5, b=1, c=21, so

now take only the positive solution since t>0 (note this will be the minus square root since we are dividing by a neagtive)

b)now this is the part that may not be correct
try to complete the square


so h=-0.1 and k=21.05 ( i dont know how h=0.1 and k=21.05 since it wont expand out to give the equation, so it should be a typo)
c) so when y=2 and t>0
just let equation equal 0 and use quadratic formula so