the answer is
a) 1000=-16t^2+1700, implies t² = -700 /-16, and t= 6.61s
b) 970= -16t^2+1700, implies t² = -730 /-16, and t=6.75s
c)
reasonable domain of h
h is polynomial function, so its domain is R, (all real number)
its range
the inverse of h is h^-1 = sqrt (1700- t / 16), and its domain is
1700- t / 16>=0, so t <1700,
the range of h is I= ]-infinity, 1700]