Because you are asking about rational equations, I read this as…
4 = 10 + 3
--- ---- ----
3x 3 x
which greatly affects the answer.
Multiply everything by 3x to get the same denominator across the board.
4 = 10x + 9
Now, it’s just a simple equation… not quadratic.
Subtract 9 from both sides.
-5 = 10x
Divide by 10.
x = -5/10 = -1/2
Plug back into your original problem to make sure it will NOT make any denominator 0, which it doesn’t. Valid solution, check!