[ShadowAce]

X=-1

Add 4x to both sides:

3=10x+13

Subtract 13 from both sides

-10=10x

Divide by 10: -1=x

[mason-dixon]

After solving ( X = -1), then put it into the original equation to check your work.

3 - 4x = 6x + 13
3 - 4*-1 = 6*-1 + 13
3 +4 = -6 + 13
7 = 7

[FlyingEagle]

Either you are right, or else the answer is 42.