How is solving an equation in the form ax^2=c similar to solving and equation in the form ax^2+b=c? How are they different?

Mahnoor randomly selects times to walk into a local restaurant and observe the type of music being played she found that the restaurant was playing country 11 times rock & roll 17 times and blues 8 times use the observed frequencies to create a probability model for the type of music the restaurant is playing the next time mahnoor walks in.