Let x be the number of books. Each book costs $19, so total price of the books is 19*x = 19x. In addition, there's a $15 shipping charge added to the total price of the books. So we get the equation 19x + 15.
Lannie ordered 12 copies of the same book, so x = 12.
19*12 + 15 = 228 + 15 = 243.
So the total cost Lannie has to pay is $243.
Hope this helps! :)