This spell functions as Magic Missile, but the caster gets 3 "lances" they can cast at a single target or up to 3 targets in a 30° cone. There is no saving throw. If the target is visible to the caster they are hit. Each lance does 17d6+1 points of damage evenly divided between Force damage, and Sonic Damage. (This will hit anything with at least half damage, as it's basically impossible to be immune to both at the same time)
That's assuming all attacks hit. Typically you'll hit 65% of attacks against level-appropriate monsters, but you also have to factor the 5% crit chance. So the average damage is 153. Which has a good chance of killing any single target unless it's a boss.
Remember that a lot of stuff, especially attacks, are abstracted in the rules. An attack roll isn't necessarily a single swing of a weapon, and a single swing isn't necessarily just one attack roll. It's more of a measure of how effective your attack(s) is/are within a given timeframe.