The forelimb structure seen in both bat wings and human arms is very similar to that of an extinct land animal called eusthenopteron. this fact suggests that

  The fact that both the humans and the bats have very similar forelimb structure, the humans in the arms, the bats in their wings, which in turn is very similar to those of an ancient sarcopterygian called eusthenopteron, suggest that both species probably share a common distant ancestor.

  The eusthenopteron was an ancient species first thought to be living on land, though the latest research shows that it was only living in water, however, this animal is a distant ancestor of both species. This animal can be seen as ancestor to the humans and the bats because it is part of group that created the first animals on land, which in turn gave rise to the mammals later on, and both humans and bats are mammals, thus there's a connection and common ancestor of the both.

try using substitution:

x + y - 6 = x - y. (i'm not giving you the exact answer). since 0 = x - y, then sub 0 in the equation with x - y. combine your like terms, and then use inverse operations, and you'll have your answer.

: -)

multiply it by 5 in order for you to understand i cant give an exact answer.