Current flow in a series circuit with two voltage sources
it appears to me that the current generated by 35 V and 2vx will
  collide each other


It may be that you are assuming that a voltage source, whether independent or controlled, must source current, i.e., supply power to the circuit.

But, at least in ideal circuit theory, there's nothing "wrong" with a voltage source sinking current, i.e., receiving power from the circuit.

For a real world example, consider that, when a battery is being charged, the current is in the opposite direction than when the battery is being discharged.


  I would like to know how the current flows across 5 Ω resistor.


If you're planning to be an EE, don't write or say things like "current across"; current is through, voltage is across.

Now, this circuit is very easy to solve.  There are two unknowns so you need two independent equations.

For the 1st, write a KVL equation clockwise 'round the loop:

$$35V = v_x + 2v_x - v_o \rightarrow  3v_x = 35V + v_o$$

Now, you need one more independent equation.  Can you find one?