assuming that the order is
ok so
distance from greenvile to parker=29
distance from greenvile to hadley=?
distance from hadley to greenvile is 12 and 1/2 less than distance between parker and greenvile means
?=-12 and 1/2+29
add
-12 and 1/2+29=6 and 1/2
?=6 and 1/2 miles