Assume that credits is an int variable whose value is 0 or positive. write an expression whose value is "freshman" or "sophomore" or "junior" or "senior" based on the value of credits. in particular: if the value of credits is less than 30 the expression's value is "freshman"; 30—59 would be a "sophomore", 60—89 would be "junior" and 90 or more would be a "senior".