Answer:
[tex]Number\ of\ science\ books=7[/tex]
Step-by-step explanation:
[tex]Let\ number\ of\ science\ books=x\\\\Story\ books=18\\\\2\times science\ books+4=Story\ books\\\\2x+4=18\\\\Subtract\ 4\ from\ both\ the\ sides\\\\2x+4-4=18-4\\\\2x=14\\\\Divide\ both\ sides\ by\ 2\\\\\frac{2x}{2}=\frac{14}{2}\\\\x=7\\\\Number\ of\ science\ books=7[/tex]
