In a large university, 20% of the students are business majors. A random sample of 100 students

Question:

In a large university, 20% of the students are business majors. A random sample of 100 students is selected.
Compute the standard error of proportion
Probability sample contains at least 12 business majors
Probability sample contains less than 15 business majors
Probability sample contains between 12 to 14 business majors
Please show all steps. Thank you in advance.