Please answer these questions it's very urgent please

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?

Find two numbers if their sum is 91 and the ratio is 6: 7?

Ibeg you to me 20. a reaction produces 4.93 l of oxygen, but was supposed to produce 1 mol of oxygen. what is the percent yield?