Interested in public interest? You better know how to make the math work. The current equation poses two challenges for new lawyers. The increase in the cost of law school makes relatively low-paying public interest jobs a tough sell to graduates who face, in some cases, hundreds of thousands of dollars of debt. Meanwhile, public interest employers have smaller budgets than they did in the pre-2008 economy, making entry-level jobs scarce. For the first problem, a student can turn to his or her school’s Loan …