Ineed i think it may be simple but it still slips my mind dont comment unless you know the answer

Here, the lines are parallel, so the mentioned angles would be: alternate opposite angles, hence their magnitude would be equal.

So, 7x-7 = 4x + 14
7x-4x = 14+7
3x = 21
x = 21/3
x = 7

In short, Your Final Answer would be: 7

Hope this helps!

You need to set 7x-7 equal to 4x+14. 
7x-7=4x+14

Then you need to add 7 to both sides to take away the -7 on one side and only have x on that side
7x=4x+21

Then subtract 4x from both sides to have x on just one side of the equation
3x=21

Then divide both sides by 3 to get x alone and also find your answer
x=7

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