B=book
a=backpack
b=50
b=2a-20
50=2a-20
2a=75
a=37.5
it cost $37.5
Aspirin comes from the bark of the Willow tree. Ancient Egyptians used the tree bark first.
Penicillin is mold Penicillium chrysogenum<span>) and was found on fruit in 1928.
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A movement in response to gravity is called tropism.
The answer is A, a high alijah of biodiversity