continuing to use modular classrooms. The school can be expanded, or a new school can be buill to "split the load" between the schools. User benefits come from improvements in school performance for the expanded or new schools. If a new school is built, there are more benefits because more students will be able to walk to school, the average distance for those who ride the school buses will be shorter, and the schools will be smaller and more "student friendly." The disbenefits for the expanded school are due to the impact of the construction process during the school year. The interest rate is $8\%,$ and the life of each altemative is $20$ years. Which alternative should be chosen? What is the incremental ratio for the preferred alternative?

$\backslash$table$[[,$Alternative,Expand$],[$User benefits $($$M$/$yr$),2\mathrm{.}1,3\mathrm{.}1],[$User disbenefits $($$M$),0\mathrm{.}8,0],[$First cost $($$M$),8\mathrm{.}8,10\mathrm{.}4],[$Operations and mainte$-,0\mathrm{.}95,1\mathrm{.}7],[$nance $($$M$/$yr$),,]]$

$($a$)$ Use the benefit$-$cost ratio.