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Suppose I am a level 10 rogue and take a level of sorcerer, giving me the firebolt cantrip. Normally, on a successful hit, the target takes 1d10 fire damage. Furthermore, the description says:
This spell's damage increases by 1d10 when you reach 5th level (2d10), 11th level (3d10), and 17th level (4d10).
How much damage should I be rolling? 1d10, because I am a level 1 sorcerer? Or 3d10 because I have attained 11 levels?