1. Angie has been playing the violin since she was eight years old, and by the time she entered high school, she became very good at it, and was encouraged by her music teacher to step up her practice and start taking lessons by a world-class instructor. Unfortunately, the lessons with the world-class instructor cost $200 per hour, more than four times what her parents were paying. When Angie's wealthy grandparents learned about this, her grandfather said to her: "Nothing but the best for you, my dear grandchild. I will pay for your lessons and will send you a check for $20,000 tomorrow. 
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3. That will be enough for 100 lessons." Angie thanked him and said, "Grandpa, when I become the world's greatest violinist, I'll always save you the best seat in the house!" To this, her grandfather replied, "That would be wonderful! I accept and will hold you to it!". Assuming capacity is not an issue here, do  Angie and her grandfather have a valid contract? Please explain.