Hi there! With equations like this we want to get our variable on one side and and our constant on the other.
So with 2x + 3 = -7 you'd subtract the constant 3 from both sides of the equal sign to get 2x = -10, then you'd divide both sides by 2 to get x = -5. If you double check your work by replacing x in the original equation with our answer we'd find that 2(-5) + 3 = -7 is correct.
Hope you find this helpful :)