Pls help me answer 7,8,9&,10. there trying to find if those questions are linear or non linear

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?

The sum of two numbers is 12 and their difference is 18 what are the two numbers

Jordan got 27 out of 90 correct on his test . what fraction of the marks did her get correct