y = -25x + 350
-25 represents the amount of pages she reads a day subtracting it from 350 pages since that was the starting amount the book had
350 is her initial value so it would be our y intercept
then to check if the solution is correct we can plug in 2 for x
y = -25(2) + 350
y = -50 + 350
y = 300
On day 2, she has 300 pages left since she read 50 pages.