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I lowballed it by assuming that STAB and sunlight do NOT take Special Attack into account. I'll be happy to redo the calculation with them considered, because my math is one of the lowest possible damage outcomes.
In any case, get swept kids.
159 base SA, Fireblast
110 power + STAB + sunlight = 220
220 + 159 = 379
Let's say your boy has 150 Special Defense
379 - 150 = 229
How much HP does your boy have again? Thought so.
Also, water attacks get cut by sunlight. Try again?