Answer:
-6
Explanation:
I'm not Russian (or whatever language that is) but hopefully I can help! <3
5x+12=8x+30
Move the 12 over to the other side by subtracting.
5x=8x+18
Move the 8x over to the other side by also subtracting.
-3x=18
Divide 18 by -3.
x=-6