Tustin-based MAI Basic Four reported net income of $23.8 million for the fiscal year ended Sept. 30, including an extraordinary tax credit of $989,000. That compares with net income of $9.1 million in fiscal 1986, including a $7.8 million charge for retirement of early debts. The company's fiscal 1987 revenues totaled $321 million, an increase of 14% from $281 million in fiscal 1986. Net income for the fourth quarter of fiscal 1987 was $7 million, contrasted with a loss of $2.3 million in 1986. Fourth-quarter revenues rose 21%, to $91.9 million from $75.7 million in the fourth quarter of last year. MAI manufactures business computers and information processing systems, primarily for use by small and medium-sized businesses.