What are some common errors that can occur when writing an expression in standard form?

Express in the simplest form: (x^2+9x+14/x^2-49) / (3x+6/x^2+x-56)

Can someone me with this? i’m not sure what to put for my equations.

At a pizza shop 70% of the customers order a pizza 25% of the customers order a salad and 15% of the customers order both a pizza and a salad if s customer is chosen at random what is the probability that he or she orders either a pizza or a salad