Part A)
To find the ratio, find the total amount of items and the tota amount of medium size items by adding the numbers of the columns:


Next, divide the total amount of medium size items by the total amount of items and simplify the fraction:

Therefore, the ratio is 1:4.
Part B)
To find the percentage, write the ratio in a decimal representation and multiply it by 100:

Therefore, 25% of each order will be size medium items.