From its allotment under subsection (b) for any fiscal year (and any amounts remaining available from allotments made to it for prior fiscal years), the Commissioner of Social Security shall from time to time pay to each State which has a plan approved under subsection (c) an amount equal to 75 per centum of the total sum expended under such plan (including the cost of administration of such plan) in providing medical and social services to severely handicapped individuals who are eligible for such services under the plan.