To do part B, use the equation that you wrote for part A. We need to figure out what month number March of 2020 will be; we started in January 2015 at month 1; month 2 was Feb. 2015; month 3 was Mar. 2015; etc. to month 12 at Dec. 2015. Then month 13 will be Jan. 2016; month 13+12=25 will be Jan. 2017; month 25+12=37 will be Jan. 2018; month 37+12=49 will be Jan. 2019; month 49+12=61 will be Jan. 2020; month 62 will be Feb. 2020; and month 63 will be March 2020.
63 is the number you will substitute for x in the equation you've already written for part A.
