I think that a nice way to think about this is to think of the chain rule as:
You can consider that the "dx's" just cancel out.
That means you can use standard algebra techniques to divide both sides by dy/dx so that you get:
Use the power rule to find dy/dx
dy/dx = 6x
So at x = 1, dy/dx = 6
Since you are given dy/dt = 4 then dx/dt = 4/6 or dx/dt = 2/3