Answer:
about 4.63 teaspoons
Explanation:
You can write the proportion ...
(teaspoons)/(fraction of RDA) = 1.75/0.85 = x/2.25
where x represents the unknown number of teaspoons. Multiplying by 2.25 gives you ...
x = 2.25(1.75/0.85) = 4.632...
About 4.63 teaspoons of vitamin will supply 2.25 times the RDA.
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That's between 4 5/8 and 4 2/3 teaspoons, roughly 22.8 mL.