For the cost to throw the event, we have to add $100+$500, the decorations and the DJ and then we have to add the variable for people times 5 since it is 5 per person. $100+500 = $600 and 5* n (the variable for people in the question)
We are adding the two terms so the final equation will be equal to:
600+5n
for b), we have to use the variable n for tickets times the constant 6 since it costs 6 dollars per person to enter, and that will be equal to the revenue the student council earns or R.
I believe "BY || JE" means that those two lines are congruent, which means the slope of JE would be the same as the slope of BY. So in this case the answer should be B. -1/5.