$21-11$ The PMS database has accumulated information regarding the performance of a pavement section before being overlaid as well as the performance of the overlay. The following data were recorded. Develop a linear prediction model $(PCR=a+b^{**}$ Age$)$ for the two cases. If a criterion was established that maintenance or rehabilitation should occur when the PCR reaches a value of $81,$ when should such actions take place in the two cases?

$\backslash$table$[[$Before Overlay,Overlay Performance$],[$PCR$,$Age $(yr),PCR,$Age $(yr)$