How do you know when something is being used as a symbol?

Which number is main idea form this paragraph? (1) in 1960, raising a child from birth to age 18 cost just over $25,000. (2) however, raising a child today is an expensive business. (3) the average cost now is just about $230,000. (4) housing takes the biggest chunk of money, about $70,000. (5) that is followed by the cost of food, which runs about $42,000, and following closely after that are the expenses of child care and education, transportation, health care, and clothing. (6) the cost averages out to about $12,800 a year, or about $1000 a month, to raise one child in a two-child, two-parent, middle-income family.