Whenever there are two - signs, this means it turns into a plus. So it would be -
1+2
And it would equal 3!
1/2 of 1/2 of 1/2 = 1/8.
There are 640 acres in a section, so 1/8 section = 80 acres.
_____
In surveying terms, "SW 1/2 of a section" is not a realistic specification of a piece of property.
73. you subtract 89 and 16 and that gives you your answer which is*** 73***