Tenafly Public Schools went back to the basics this week — using overhead projectors, paper, pencils and hands-on activities in classrooms — when a ransomware attack crippled the district’s computer system. Final exams were also canceled for all of the district’s high school students as the Bergen County school district tries to get its system back online with the help of cybersecurity consultants, officials said. Tenafly Public School District administrators first identified the security incident Thursday, said district communications manager Christine Corliss. It involved the encryption of d…