5x - 5 should be equal to 2x + 10, because of the property of Vertically opposite angles.
Vertically Opposite Angles or VOA says that 2 angles that are vertically opposite are the same.
So,
5x - 5 = 2x + 10
5x - 2x = 10 + 5
3x = 15
x = 15 / 3
x = 5.
Hope you understood it. If you have any doubts plz let me know.