For a. - d., you need to find two things: the gradient and a point on the line. Get those two things and substitute into where m is the gradient and is a point on the line.

You're lucky that in each case, a point on the line isgivento you. So you really only have to worry about finding m (and in c. eventhatis given to you) .....

For e., substitute the value for radius and the coordinates of centre (is that what you mean by midpoint?) into the standard equation for a circle. This equation has been stated in a reply to previous question.