A student's grade in a course is the average of 4 test grades and a final exam that is worth twice as much as each test. Suppose a student has test grades of 91, 82, 83, and 92. Write an equation to model this situation where xis the student's grade on the final exam and yis the student's average for the course.
__________

Then find the score they will need to receive on their final exam if they want to have a grade of 90 for the course.

Final exam score needed = ____________