Answer :
Answer: 3F+2F+4F+F=750
science fiction=225
mystery=150
biographies=300
fiction=75
Step-by-step explanation: To find the equation, read through the question and write down any important information, such as there are 2 twice as many mystery book as fiction books (2*fiction books=mystery books). Once you have all the information written down place it in an equation set equal to the total (750).
After you have found the equation, solve for the fiction books (F) by isolating the variable. 3F+2F+4F+F=750, 10F=750, F=750/10, F=75.
After that you plug 75 into the equation. Which would get you 3*75= 225 science fiction books 2*75= 150 mystery books and 4*75=300 biographies