You must move all constants to one side of the equation (one side of the equal sign) and away from 2x. To do so, you must do the inverse operation, which would be subtraction in this case because 3 is a positive number. (Inverse of addition is subtraction, Inverse of subtraction is addition, Inverse of multiplication is division, and inverse of division is multiplication) If you squish a constant and variable together (2x) it means multiplication.
What you must do to one side, you must do to the other. So, since you subtracted 3 from the 3, you must subtract 3 from -7, too(subtracting from a negative is just addition- but you keep the negative sign). Once this is done, your equation will be 2x=-10
Now, you must do the inverse operation to 2x to separate the 2. The inverse operation will be division. So, you divide bothsidesby 2. 2x divided by 2 will give you x. -10 divided by 2 will give you -5. (When you divided negative and positive numbers, the signs are different, meaning it's negative. If they had the same sign, it would be positive.)
