Halley’s comet appears in the sky once every 75 years. it last appeared in 1986. two students wrote expressions to find which years after 1986 the comet will appear. julian: : 75x + 75x whose expression is correct and why? a. neither expression is correct, because the correct expression is 75 + 1986x. b. both expressions are correct, because both show that the comet reappears every 75 years. c. julian’s expression is correct, because it shows that the comet reappears every 75 years. the year it last appeared doesn’t matter. d. casey’s expression is correct, because it shows that the comet reappears every 75 years after 1986.