The percentage of families that were married couples with children between 1970 and 2000 is approximately 50.5 P(t)= = +0.27 (1st4) where t is measured in decades, with t = 1 corresponding to 1970. (a) What percentage of families were married couples with children in 1980? (Round your answers to one decimal place.) ---Select--- (b) How fast was the percentage of families that were married couples with children changing in 1980? (Round your answers to one decimal place.) ---Select--