We want to know for what value of V0 will there be some time when the distance traveled will be d[xfar] and the height be 10 feet.
We want to know for what value of V0 will there be some time when the distance traveled will be d[xfar] and the height be 10 feet.
Input := Clear[V0]
Input := eq1 = horiz[t]==d[xfar];
Input := eq2 = vert[t]==10;
Input :=
s3 = Solve[{eq1,eq2},{V0,t}]
Output =
{{V0 -> -141.905, t -> -3.62763},
{V0 -> 141.905, t -> 3.62763}}
Clearly the second solution is the one!
Input := V0 = s3[[2,1,2]];