What is the ratio of quarters to nickels in a dollar

How can you find the conditional probability of a given b as the fraction of b’s outcomes that also belong to a, and interpret the answer in terms of the model? i just need a good explanation

At a sale this week, a desk is being sold for $213. this is a 29% discount from the original price. what is the original price?

Can you me find the missing length. i attached an image.