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Of the divisors of 90, how many are not divisible by 9?
Literal
90 [possessive-の] divisors [out of-のうち], 9 [with-で] cannot-be-divided numbers [topic-は] how-many [subject-(omitted)] exist [wondering-でしょうか].
A math word problem. 約数 is 'divisor' in the mathematical sense (a number that divides another evenly). 割り切れる is the potential of 割り切る — 'to be able to divide completely/cleanly' — and specifically used in math for 'divisible'. The counter 個 counts abstract or small items, including numbers in this sort of problem. でしょうか is the polite uncertain-interrogative ending used in classroom/textbook prompts.