3×+4=-17 is an equation i don't understand

It is an equation, since it has many operations in it, and importantly, it has an equal sign. EQUation.

Alright, so what you're going to want to do is subtract 4 from both sides of the equation.
-3x + 4 - 4 = -17 - 4 = -3x = -21

No divide -21 by -3.
Since a negative number divided by another negative number is always positive, your answer is x = 7

The first option would be correct if it were one half and not one