do I understand this right?(Wondering)

Find the centroid of the region bounded by the graphs of the equations:

y = 2x

x = 2y

x = 6

Area of region = integral from 0 to 6 [2x-1/2x] dx

A = 27

what does this "x[" come from?

x = 1/A integral from 0 to 6 x[(2x)-(1.2)]dx

x = 4

y = 1/A integral from 0 to 6 [(2x+1/2x)/2][(2x)-(1/2x)] dx

y = 5