(1) Every wage earner covered under the Social Security Act pays a tax; the employer also pays a tax, which is equal to that paid by the employee. (2) The amount that one can expect to receive each month in old-age insurance benefits depends on one's average monthly earnings. (3) Also, the size of the benefits depends on the number of years one has worked. (4) If a person retires at 65, the monthly benefits are greater than if he or she retires at 62. (5) These benefits are a retirement annuity. (6) In other words, they are paid to the wage earner from the date of retirement to the time he or she dies. (7) In addition, when a wage earner dies, Social Security provides payments to his or her spouse, to dependent parents, and to children until they are about 18 years of age (21 if they are in school). (8) Further, payments are made to a wage earner (and dependents) if he or she is totally disabled and unable to work.

The implied main idea of the selection is

a) President Roosevelt, in 1935, signed into law the Social Security Act. It is a federal law that provides for the general welfare of citizens through the provision of old-age benefits. It also provides social insurance for blind persons, dependent and disabled children, maternal and child welfare, public health, and unemployment.

b) The main idea is represented by the topic sentence. It introduces the theme of a passage. It is supported by other ideas that provide evidence and examples. This function is ably and accurately performed by sentences 2 to 8 in this passage.