Final answer:
The method call letterGrade(doubleAverage); could be incorrect if the method name or parameter is wrong, if it requires an object or class to be invoked, or if doubleAverage isn't defined or of the correct data type.
Step-by-step explanation:
The issue with the method call letterGrade(doubleAverage); could be due to a number of reasons. It may be a syntactical error related to the method name or the parameter. In some programming languages, the method call syntax requires an object or class name before the method. For example, in Java, if letterGrade is an instance method, it should be called through an object: objectName.letterGrade(doubleAverage);. If it's a static method, it should be called with a class name: ClassName.letterGrade(doubleAverage);. There could also be an error if doubleAverage is not a previously defined variable or is not of the correct data type expected by the method.