Problem 1
One possible answer is y = -x+5
This equation has a slope of -1 as does the first equation y = -x+3. Parallel lines have equal slopes but different y intercepts.
You can change the "+5" to any number you want.
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Problem 2
One possible answer is y = (3/4)x - 2. Like before, parallel lines have the same slope, just a different y intercept. The "-2" can be any number (negative or positive) you want as long as the slope remains 3/4.