Estimating instananeous rates of change from equations

A diver is on the 10 m platform, preparing to perform a dive. The diver's height above the water, in metres, at time t can be modelled using the equation h(t) = 10 + 2h - 4.9t^2

(a) determine when the diver will enter the water

(b) estimate the rate at which the diver's height above the water is changing as the diver enters the water

2h should be 2t, otherwise it does not make sense, it represents the constant velocity

a) solve h(t) = 0

10 + 2t - 4.9t² = 0

t = 1.647 s

b) take the derivative and plug in 1.647 s

dh/dt = 2 - 9.8 t
dh/dt = 2 - 9.8 (1.647 ) = -14.14 m/s

B)Rate is answer to part a in the equation rate= -4.9t+2 (derivative of equation)
A) use a graphing calculator or kinematic equations solving for time without velocity final.