Your first two interpretations aren't correct. Your third interpretation is.
Once you interpret the first two quantities in the way that the third was, you should see where your mistake lies.
But, for completeness:
The phrase "The ratio of $A$ to $B$" refers to the quotient $A/B$.
I think it's better not to use decimals here, but rather say, for example, "the ratio of $A$ to $B$ is $1:9$ (one to nine)". This would mean that for every $9$ units of $B$ sold, one unit of $A$ was sold (this is the manner in which the information for 2020 is phrased).
If you wanted the percentage of the total amount ($A+B$) that $A$ is, it would be expressed as a decimal as $A\over A+B$. If the ratio $A$ to $B$ is given as a decimal $x$, then the percentage of the total that $A$ is would be expressed as a decimal using the formula ${x\over x+1}$.
For example, in 2009, the ratio of sausages to burgers was $x=.11\approx1/9$. The percentage of sausages sold in 2009 was $ {1/9\over 1+1/9} ={1\over9+1}={1\over 10}$. So the percentage is $ 10\%$.
This should make sense, as you can do the computation somewhat differently:
In 2009, for every $9$ burgers sold, $1$ sausage was sold (here, you just make up numbers that give the correct ratio). So the percentage of sausage sold in 2009 was ${1\over 1+9}\cdot 100\% =10\%$ (part to the whole).
Best Answer
It should be $$4 \times 8^0 + 5 \times 8^{-1} = 4.625$$
and not what you are doing. You should simply multiply each digit in the number with the radix raised to the correct power, which is $0,1,2, ...$ for the digits to the left of the decimal point and $-1, -2, -3, ...$ for the digits to the right of the decimal point.