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x = first y = second
x - y = 33 (1) according to the condition
y = 3x-7 (2) according to the condition
Substitute (2) into (1) to get
x - (3x-7) = 33
x - 3x + 7 = 33
-2x = 33 - 7
-2x = 26
x = -13 ====> y = 3x-7 = 3*(-13) - 7 = -39-7 = -46.
Answer. The numbers are -13 (first) and -46 (second).
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Notice: The words "the difference of two numbers" may mean (x-y) OR (y-x) - it is not determined by an unique way.
So, playing with the difference y-x = 33, you will get another answer.
Try it and get your own answer/solution.