projectile launch velocities, given a position

struggling with this problem:

using very simple projectile rules (no air resistance ect) and only gravity acting on the object, is it possible to:

with a known: gravity, launch magnatude and coodinates which the partical passes through, to work out the launch angle (or x,y components?)

using the position equations:

X=Vx*t

Y=Vy*t+(g/2)*t^2

how do i find Vx and Vy?

itld be easy if i knew time, but i dont, however i do know magnatude.

sqrt(Vx^2+Vy^2)=M

anyone got any ideas?