In your class, you have scores of $69,70,83,$ and $86$ on the first four of five tests. To get a grade of $C,$ the average of the first five tests scores must be greater than or equal to $70$ and less than $80.$

a$.$ Solve an inequality to find the least score you can get on the last test and still earn a C$.$

b$.$ What score do you need if the fifth test counts as two tests?

a$.$ The least score you need on the last test to get a $C$ is