SOLUTION: Hello I am trying to do my math homework and there are still questions that I just don't understand. I would greatly appreciate being walked through the following problems because

Question 820632: Hello I am trying to do my math homework and there are still questions that I just don't understand. I would greatly appreciate being walked through the following problems because at this point I really don't think I can get the answer on my own. Here are the problems

Use substitution to solve each system of equations. If the system does not have exactly one solution, state whether is has no solution or infinitely many.
18. 2x-y=-4
-3x+y=-9
20. 2x+3y=1
-3x+y=15
22. 5r-s=5
-4r+5s=17
24. x-3y=0
3x+y=7
26. 0.5x-2y=17
2x+y=104
28. x=1/2y+3
2x-y=6
Please help me, I am so lost. Thank you
Answer by Alan3354(69443) (Show Source): You can put this solution on YOUR website!
Use substitution to solve each system of equations. If the system does not have exactly one solution, state whether is has no solution or infinitely many.
18. 2x-y=-4
-3x+y=-9
--------------
Solve either equation for 1 of the variables, either x or y.
2x-y=-4 =
y = 2x+4
---
Sub for y in the other equation
-3x+y=-9
-3x+ (2x+4) = -9
-x + 4 = -9
x = 13
---
Sub for x in any eqn to find y.
y = 2x+4
y = 2*13 + 4
y = 30
===================
That's all.
----------------
20. 2x+3y=1
-3x+y=15
Solve for the one that's most convenient - y in the 2nd equation.
------
22. 5r-s=5
-4r+5s=17
Same as above
24. x-3y=0
3x+y=7
26. 0.5x-2y=17
2x+y=104
28. x=1/2y+3
2x-y=6

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