Solving Equations: 3x + (-3) = x + 199, -300 -(-4x) = + -8x

[Gringo123]

I have just been doing some algebra homework. The are just problems that I can't work out. I wonder if anyone can explain how to solve them?

3x + (-3) = x + 199
x = ?
I know the answer is x = 101 but I haven't worked it out in the right way. I just did it by deduction which took ages. What is the right way to tackle this problem?

I have the same problem with this one. I know that x = 25 but how do you work it out?

-300 -(-4x) = + -8x

 

[Mentallic]

$$3x-3=x+199$$

You're trying to solve for x so the ultimate goal here is to move all the x onto one side of the equation, and then simplify to isolate it, x=...

$$-300-(-4x)=\pm 8x$$

Is that actually meant to be a $\pm$? Because if so, the difficulty between the first and second equation is pretty significant. Unless of course I misread the first equation?

Anyway, you can do this by mainly two ways:
1) square both sides and solve the quadratic
2) Take separate cases, first use 8x and then -8x

Oh and you do realize that $-(-4x)=4x$, right?