Your grades on three exams are 80, 93, and 91. What grade would you need on your next exam to have an average of 88 on the four exams?
Let the grade on the next exam be represented by x.
To have an average of 88 on the four exams, the sum of the grades on the four exams would be 4 * 88 = <<4*88=352>>352.
The sum of the grades on the first three exams is 80 + 93 + 91 = <<80+93+91=264>>264.
Therefore, the grade needed on the next exam to have an average of 88 on the four exams would be 352 - 264 = <<352-264=88>>88. Answer: \boxed{88}.