One of my classmates ask this question and it wasn't answered so now I am asking it and of course we are all struggling with no strong Math background

Question

Case 6.4 Maternal Serum Screening Test for Down syndrome
Please keep in mind that I do not have a Math back ground so this is brand new to me and like a foreign language that I have never seen nor heard spoken before. Thank you for your help in advance.

Pregnant women are screened for a birth defect called Down syndrome. Down syndrome babies are mentally and physically challenged. Some mothers choose to abort the fetus when they are certain that their baby will be born with the syndrome. The most common screening is maternal Serum screening, a blood test that looks for markers in the blood to indicate whether the birth defects may occur. The false- positive and false- Negative rates vary according to the mother.
Mothers age false positive rate false negative rate
Under 30 .04 .376
30-34 .082 .290
35-37 .178 .269
Over 38 .343 .029
The probability that the baby has Down syndrome is primarily a function of the mother’s age. The probabilities are listed here.
Age Probability of Down Syndrome
25 1/1300
30 1/900
35 1/350
40 1/100
45 1/25
49 1/12
a) For each of the ages 25, 30, 35, 40, 45, and 49, determine the probability of Down syndrome if the maternity serum screening produces a positive result.
b) Repeat the negative result