Gillian purchased 25 books at the library book sale. each hardcover book cost $1.50, and each paperback book cost $0.50. gillian spent a total of $26.50. the book costs can be represented by the system of equations below.

h + p = 25.
1.50h + 0.50p = 26.50

how many paperback books did gillian buy?

The system of linear equations that best represent the given is already shown above. Express the p of the first equation in terms of h and substitute this expression to the second equation. That is,
                           1.50h + 0.5(25 - h) = 26.50
The value of h from the equation above is 14. Thus, the number of paperback books that Gillian bought, p, is 11. 

H + p = 25
h = 25 - p
so we sub 25 - p in for h in the other equation

1.50h + 0.50p = 26.50
1.50(25 - p) + 0.50p = 26.50
37.50 - 1.50p + 0.50p = 26.50
- p = 26.50 - 37.50
-p = -11
p = 11 <== Gillian bought 11 paperbacks (p)

Cwill be your correct answer