A 3.50 gram bullet is fired horizontally at two blocks resting on a smooth surface. The bullet passes through the first block, with mass 1.20 kilogram and embeds itself in the second block, with mass 1.80 kilogram. The first block has a velocity of 0.630 m/s after the bullet passes through it. The second block has a velocity of 1.40 m/s with the bullet embedded in it. Ignore the mass removed from the first block as the bullet passes through. Estimate what is the initial speed of the bullet?