Question 973324
So the variables are s and t instead of x and y.  What is stopping you?  You use the same skills and concepts, no matter what pair of variables are in the equations' system.



...... NOW I see.
Your number lines are for variables named differently, such as the t axis and the s axis.



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Your other question:  No.  Your variables are s and t.  Also you are not justified in changing either of the equations.  One of your variables will be used for the horizontal coordinate, and the other of your variables will be used for the vertical coordinate.