match each expression to its simplest form
(6r+7)+(13+7r)
(13 - 3/2 r) - (1 - r)
(-8 - r) + (2r - 4)
(7r - 3/2) -(2/3 + 6r)

12 - 1/2 r --------→
r - 13/6 ---------→
13r+20 -------→
—12+r ---------→​