First, is he used 29 out of the 547 for a park, he can't use them for two acre building lots, so we must subtract:
547-29 = 518
If we want to know how many 2 acre building lots we can sell, we can divide 518 by 2, as dividing it by 2 sees how many times 2 goes into 518- essentially how many two acre lots are in 518 acres.
