The cost of 18 notebooks at store j is $22.50. The notebooks at store j are all same price. The cost of notebooks at store k is shown on the graph below

Aclassmate thinks that solving a system by graphing gives an exact answer when the lines appear to cross at a grid point, but only an approximate answer when they don't. explain why this isn't true.

Select the correct answer and solve for y

What is the area of the shaded sector?