[clivehawkins]

Hi there,
I'm afraid I can't help with the grades thing, but I can explain a couple of the infinitives used in your examples.

"I use a computer to play games." - this is an example of the infinitive of purpose ie to say why you do something. eg I went to Spain (why?) to see a bullfight, I listen to audiobooks (why?) to improve my English.

"I want to find some e-pals." here 'want' is an example of one of the verbs that takes the infinitive. Other examples are would like, need, hope, plan, decide. There are quite a few!

"We are glad to have a chance." - this is the infinitive used after adjectives. Other examples, pleased to meet you, I'm upset to hear . . . ., She was delighted to see you, It's easy to make a mistake, etc.

As for the final example you give, I'm sorry to say (infinitive after adjective :-) ) that I can't think of the reason why it's infinitive.
In any case, hope that helps. have a good day.