Do do this problem, and others like it, you need to get rid of the radical!
To do that you need to square both sides:
Squaring a Radical will remove the Radical!
So you are left with:
5x - 7 = 3x + 5
2x - 7 = 5
2x = 12
x = 6
So your answer is x = 6
I hope this helps!