Calculating Total Savings After Weeks

Sarah is saving money to buy a new bicycle. She starts with $50 and plans to save $10 each week.

If we let $x$ represent the number of weeks Sarah saves money, we can write an equation to represent her total savings $S$ after $x$ weeks.

What is the expression for $S$ in terms of $x$, and how much money will Sarah have after saving for 3 weeks?