I'm having trouble understanding how I'm supposed to answer part a of this question I'm on. I was able to do b, c, d, and e though.

Problem: The U.S. government has devoted considerable funding to missile defense research over the past 20 years. The latest development is the Space-Based Infrared System (SBIRS), which uses satellite imagery to detect and track missiles. The probability that an intruding object will be detected on a flight track by SBIRS is .8. Consider a sample of 20 simulated tracks, each with an intruding object. Let x equal the number of these tracks on which SBIRS detects the object.

a. Demonstrate that x is (approximately) a binomial random variable.

So, I'm just having a lot of trouble understanding how I'm supposed to demonstrate this and it would be great if someone could explain it to me.