x-dir
Vx=v0*Cos[theta]
?d=R=100(* meters*)
?t=t
Vx=?d/?t
v0*Cos[theta]=?d/?t=R/t
t=R/v0*Cos[theta]
y-dir
Vy=v0*Sin[theta]
a=-g
?d=b=50(* meters*)
?t=t
?d=v*t+1/2*a t^2
b=v0*Sin[theta]*t-g/2*t^2
then :
b=v0*Sin[theta]*(R/v0*Cos[theta])-g/2*(R/v0*Cos[theta])^2
and then:
v0 = 930; R = 100; b = 50; g = 9.8;
sol = Theta /. Solve[b == R*Tan[Theta] - g/2*(R/(v0*Cos[Theta]))^2, Theta] /. C[1] -> 0
(* {-2.67738, -1.57136, 0.464214, 1.57023}*)
{sol[[3]]/Degree // N // DMSString, sol[[4]]/Degree // N // DMSString}
(* 26°35'51.075" or 89°58'3.110" *)
Reference.
With high speed bullet and for a very short distance formula is very easy:
R = 100;
b = 50;
ArcTan[b/R]/Degree // N // DMSString
(* 26°33'54.184'' *)