What can I do if I juts purchase vehicle less then 50 days ago and now transmission needs repair?

Did it have a warranty? Did you buy it as is? Did they claim the transmission was great? All these questions need to be answered in order to address this issue.

It depends. If you purchased the car with an "as is" warranty, there is generally nothing that you can do under contract law. If the car is new or was used and carried some type of warranty, then you can require the dealership or seller to repair the carat no cost. If there is no warranty issue at all, your only hope is that your situation would be appropriate for California's "lemon laws", which offer some protection if a car is intentionally shown to be defective, but not represented as such.

Depends upon the terms of the purchase. Is this a new car, is it a used car, are their any warranties?

If you purchased your vehicle "AS IS" (i.e., without a warranty), then unless you can prove fraud in the purchase of the vehicle, you are on the hook for the repairs. You will not, however, be off the hook for the contract requiring you to pay for the vehicle.

You should have the "as is" vehicle to be checked out before you purchased it.