Question 1: Bring Y=2X into X+Y= 12 to get X+2X= 12 and get X=4. Substituting X=4 into Y=2X gives Y=8.

Question 2: Bring X=Y-5/2 in the following formula into 4Y- 10+3Y=65 and get Y=75/7. Bring Y=75/7 into X=Y-5/2, and you get.

X= 1 15/ 14

Question 3: Bring the deformed X=7+Y from X-Y=7 into X+Y= 1 1 to get 7+Y =1,the solution will be Y=2, and X=7+Y will be X=9.

Question 4: Bring the deformation of X+2Y=3, X=3-2Y into 3X-2Y=9 to get 9-6Y-2Y=9, Y=0, and X=3-2Y to get 3.