Reimbursement for the necessary costs of special education programs and services shall be a portion determined by the amount allocated under section 51a(1), but not to exceed 75% of the total approved costs of operating special education programs and services approved by the department and included or applying for inclusion in the intermediate district plan adopted pursuant to article 3 of the revised school code, MCL 380.1701 to 380.1766, for special education pupils other than those programs funded under section 53a, and of the costs of summer programs and services and the costs of providing room and board for special education pupils, as approved by the department. If the state financed proportion of reimbursement of the necessary costs of a special education activity or service required by article 3 of the revised school code, MCL 380.1701 to 380.1766, which is in addition to or different from the special education activities or services required under section 611 to 620 of part B of the individuals with disabilities education act, title VI of Public Law 91-230, 20 U.S.C. § 1411 to 1420, is less than the state financed proportion of the necessary costs of that activity or service in 1978-79, the portion of the amount appropriated shall be increased to reimburse that activity or service accordingly.