help this probability and statistic question with clear steps, thank you so much

(a) A family has 3 children. Let *gbb" indicate that the first child is a girl and the second and third children are boys. Similarly, 'bgb' indicates that the first child is a boy, the second is a girl and the third is a boy. Suppose that each child is born is equally likely to be a boy or girl. (i) List all event space. Hence calculate the probability that the family has only one boy. (5 marks) (ii) What is the probability that the family has at least two girls? (2 marks) (b) A combination secret lock requires three selections of numbers. Each selection is from 1 to 20 inclusive. (i) How many different combinations are possible? (2 marks) (ii) Suppose that the lock is built so that no number can be used more than once. How many different combinations are possible then? (2 marks)