The ratio of carrots to parsnips is 9:5.
To find the answer to the second question write the ratio as an fraction and equal it to the number of carrots over the number of parsnips.
Ratio: 9/5
Number of Carrots: 27
Number of Parsnips: x
Equation: 9/5 = 27/x
Cross multiply--- 9x = 27*5
Simplify--- 9x = 135
Simplify--- (9x)/9 = 135/9
Simplify--- x = 15
If there are 27 carrots, Oscar needs to use 15 parsnips for the vegetable soup.