Can someone help i don't get this problem

Data are collected to see how many ice-cream cones are sold at a ballpark in a week. day 1 is sunday and day 7 is the following saturday. use the data from the table to create a scatter plot.

The pyramid below was dissected by a horizontal plane which shape describes the pyramid horizontal cross section

How do i i solve this equation? -18 = x/3 + 3