Ok so im a little stressed out I have an exam on thurs and no idea about this stuff. This was the example on the practice examination! HELP

scientists believe that 40% of industries are heavy polluters. They found that 30 out of 80 are heavy polluters.

ok so here is what i need help with,

What is the variable?

what hypothesis test do i need to do??

and if i have a 95% confidance interval, (standard error of 0.05), what sample size do i need??

Im Lost!