I NEED HELP I'm behind and i don't know how to do chi-square equations

Which of the following is a period in the paleozoic era? devonian cambrian permian all of the above

[34 points awarded to the best answer, use facts and/or data] 1.) what's the likelihood of thunderstorms occurring in the state of maryland? {this question is for a project for science, use facts and/or data and explain why . 34 points to the best answer]

Ascientist is investigating the effects of salinity on fish development. he places fertilized fish eggs in an aquarium that contains low salinity and observes their development. what factor would improve experimental design the most? place the fish eggs in the open ocean because that is the natural habitat include another aquarium that has normal salinity to compare to the low salinity aquarium include an aquarium that replaces salt with sugar to confirm that the effects are specific to salt grow algae with the fish eggs in order to provide adequate nutrients to the developing embryos