Can someone please help with my math real quick?

Giuseppi's pizza had orders for $931.00 of pizzas. the prices were $21 for a large pizza, 514 for a medium pizza, and $7 for a small pizza. the number of large pizzas was two less than four times the number of medium pizzas. thenumber of small pizzas was three more than three times the number of medium pizzas. how many of each size of pizza were ordered?

What are the coordinates of the point that is 1/3 of the way from a to b? a (2,-3) b (2,6)

Having a hard time understanding this question (see attachment).