S.20 1-4

a) 14
b) 28, 29, 30
c) 14, 15, 16
d)
 A_r=\frac{27{,}976927\cdot92{,}23+28{,}976495\cdot4{,}67+29{,}973770\cdot3{,}10}{100}
=28{,}0855...\approx28{,}086