Two point masses are on the x-axis: a 3kg mass at x=0 and a 2kg mass at x=5m. The 2kg mass is then moved to x=7m while the 3kg mass remains fixed. What is the new x-coordinate of the center of mass of the two-mass system?
a) 2.0m
b) 3.5m
c) 2.8m
d) 4.2m