Why calculate the variance covariance matrix for a portfolio

According to the national center for health statistics, in 1990, 28 % of babies in the united states were born to parents who were not married. throughout the 1990s, this increased by approximately 0.6 % per year. if this trend continues, in which year will 52 % of babies be born out of wedlock? in__52 % of babies will be born out of wedlock