Solve each system without graphing 2d = 8f, 18 - 4f = 2d, find a substitute

Hi, can anyone show me how to do this problem? 100 points for this. in advance

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?

Two years ago a man was six times as old as his daughter. in 18 years he will be twice as old as his daughter. determine their present ages.