Hi Daniol10! Welcome to PF!

(try using the X_{2} button just above the Reply box )
ok, so you have an equation d = 96 + 80t - 16t

^{2},

and you need to sove it for (a) d = 0, and (b) d = 96.

sooo … just put that value of d into the equation, and solve it as an ordinary quadratic equation in t …

what do you get?