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
