exam Maths Puzzle Numerical Ability

i dont get 2=3x-13.
i really dont get the inverse.

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exam Other Question

3 times a number, increased by 7, is 19. Find the number. solve the system by graphing
x+y=3
x+y= -1

My question is do I just pick a number to plug in for x & y or do I use the 3 and 1 somehow?