formal or informal(10)

Question: Tell which of the two sentences in each group is formal and which is informal. 7. a. He’s older than me. b. He is older than I. 8. a. Much higher altitudes were achieved by this method. b. This method achieved much higher altitudes. 9. a. It is more time that we need. b. We need more time. 10. a. Living in the country, we had few social visits. b. We lived in the country, so nobody visited us.