For the graph: you can draw a line about 15cm, put 0 at the start then after 5cm put 5 then 10 at 10cm and 15 at the end. At 5 put • that's the starting and go all the way to 15 and add > to show that the line continues. I'm not good at explaining but I hope it helps.
The answer to your question is x – 56.64 = 3.36; x = 60 because He gave the cashier 60 dollars, and the cashier game him back 3.36 dollars. And 60-$56.64 = $3.36.