Bob offers Ben $50 per week to mow his lawn every Saturday. Ben agrees to provide the mower, gas, and oil. Bob says he will pay Ben in two installments at six weeks, and if the job is satisfactory, the second payment will be at 12 weeks. Ben accepts the offer and mows the lawn every Saturday. After six weeks, Ben goes to collect the first installment and finds out Bob left the day before on a three-week camping trip. Assuming Bob just forgot about the due date, Ben continues to mow for another three weeks. Bob returns and refuses to pay claiming that he did not make the payment after six weeks because he was dissatisfied with the work and he is not going to pay for the other three weeks either. Bob is 60 years old. Ben is 14. Does this situation describe an offer and acceptance sufficient for a valid contract and if no please explain why?