Alexa owns a total of 45 fiction and nonfiction books. if the number of fiction books is 15 more than 4 times the number of nonfiction books, how many fiction books does she own?
a)42 b)39
c)36 d)33

Let’s call x the number of fiction books and y the number of nonfiction book

x+y=45
x=4y+15

solve by substitution, you know the x value, plug it into the first equation.

(4y+15)+y=45
5y+15 = 45
5y=30
y=6

use y to solve for x
x+6=45
x=41

alexa has 41 fiction books and 6 nonfiction books