There's no definitive way to answer this question. You're going to have to estimate and provide references for how you created the estimate. A few things to consider:
How many humans were on the planet on 1/1/70? What is today's population? Was the population growth linear, exponential, etc.? Were there any discontinuities (e.g. wartime)?
What is the average weight of human hair? Has that average weight changed over time? Do you need to consider hair on the head or hair on the whole body?
How fast does human hair deteriorate? Does it last more than 50 years?
Do you need to write a program for this? I see that the topic was computer science. Do you need to create graphics?
