20 divided by 0 isn’t possible :)
which is similar to n:1 where 
<u>Step-by-step explanation:</u>
Here we have to Express in the form n:1 give n as a decimal 21:12 . Let's find out:
Given ratio as 21:12 . Let's convert it into n:1 , where n is decimal
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{ dividing denominator & numerator by 4 }
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which is similar to n:1 where 
Answer 2.85
On rounding to nearest hundredths, we get than 2.85 as at thousandths place, there is 9 which is greater than 5, so 1 is added to the hundredth value.
150 / 12 = 11.6666666667
11.6666666667 x 30 = approximately 350g of flour for 30 cakes