Upon a flat only 10 m high (Is that possible?) there are two guns A and B attached together making a vertical angle of 60 degrees when A is flat on roof. They fire at the same time and has the same reloading time. Both guns are capable of giving an initial velocity of 5√3 to their bullets. If the 2nd bullet of A hits the 1st bullet of B in mid air, what's the reload time?

You have to figure where they hit. They ave the same horizontal distance, and same vertical final height at times separated by reload time.

Vertical poistion:
A) h=10-1/2 g (t-R)^2 where t is time in air of B, and R is reloadt time.
B) h=10-5sqrt3sin60*t
That t puts them at the same vertical height. So you have three unknowns, vertical height, t, and R. You have two equa;tions.
Now considerhorizontal distance.
A) d=5sqrt3*(t-R)
B) d=5sqrt3*cos60*t
set these two eqaul to get
t-R=cos60t or 1.5t=R
Now you have three equations, three unknowns.
Have fun with the algebra. It should work out quickly.