After simplifying, which three expressions are equivalent?

a. (3.4a−1.7b)
b. (2.5a−3.9b)
c. (2.5a+1.6b)
d. (3.4a+4b)
e. (−3.9b+a)
f. (−1.7b+4.9a)
g. −0.4b
h. (6b−5.9a)
i. 5.9a−5.6b