Use "couldnt" in a sentence

1. No chance of me finishing.' 'completely Butchered that pint, couldnt even down it.'

2. I looked on the wiki math symbol page and couldnt find one, so Im thinking "Corresponds" is wrong word

3. I tried to built a car with wheels Attacht on a rotor Now the Problem is that i couldnt steer the wheel with the Cockpit because they Attacht to a rotor

4. Behindhand Renege-they had agreed that the house rent would be collected every 6 months-but he couldnt pay what his house owners demanded even after two years so was given a one month notice