Please help I will award brainless to whoever helps please it’s urgent

Can you me find the missing length. i attached an image.

9is the geometric mean between x and 12

15. jiovanni is looking in to two different companies that offer study guides for math exams.test prep 101 charges a $5 flat fee and an additional $0.25 per problem.math charges a $2 flat fee and an additional $0.50 per problem.how many prablems would make the costs of the two companies be equal? varibles: equations/eniqualities{ {