Pls help i need this to pass algebra

This is algebra, so the first step would be to combine like terms. Instead of adding 3x to 7x like they should’ve, they instead subtracted 3 from 5 ignoring the fact that they’re different numbers on different sides of the equation.

7x + 3x = 10
5 - 21 = -16
Now you have 10x = -16.
-16/10 = -1.6
So x=-1.6

Judging by how this is formatted however, x=-16/10

The correct answer is 10%