In the equation of a straight line (when the equation is written as "y = mx + b"), the slope is the number "m" that is multiplied on the x, and "b" is the y-intercept (that is, the point where the line crosses the vertical y-axis). This useful form of the line equation is sensibly named the "slope-intercept form"
Start by finding out how many books per shelf. So divide 48 by 6, which would mean 8 books per shelf. Multiply this by 12 shelves, which gives you 96 books. Hope this helps!!