You have the following algebraic expression:
8x + 6 - 5x - 4
In order to simplify the previous expression, you take into account that you only can add or subtract similar terms. Similar terms are those ones with the same variable and same exponent, and also independent numbers are similar.
Then, you have:
8x + 6 - 5x - 4
= 8x - 5x + 6 - 4
= 3x + 2
Hence, the simplified expression is 3x + 2