Is x^(-3/7) equivalent to 7th root of (1/(x^3))

Answer pls man im trying to get out of summer school

Ineed big ! the cost of a school banquet is $25 plus $15 for each person attending. create a table, sketch the graph, and write an equation in slope-intercept and point-slope form that gives total cost as a function of the number of people attending. what is the cost for 77 people?

Math i have no idea how to do a and b