What is a simplified expression for the model

The last time i bought this product , it cost $20.00 but it looks like it cost 29. 60 today? what is the increase

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?

For how answer my question this will be the last question can you answer in math subject