You do not want to choose a job solely because it will result in the largest profits, but money is definitely a factor one should consider when choosing a major.
When you participate in a degree program, you are sinking a fair amount of time and effort into one career path. Logically, you would want to make sure that your investment paid off and you were someday able to afford a comfortable life for yourself. No one wants to go into student loan debt and study for 4-12 years to make 3 dollars more than the high school dropout who works at the gas station.
A hexagon has six sides. If it is a regular hexagon, then it is equilateral, meaning that each side is the same length. If one side is 7.8cm, then all sides will be 7.8cm. You can find the perimeter by adding 7.8 six times, or multiplying 7.8 by six.