Question 13332
First of all, you need to set up equations to fit the problem.  I have added these to your question.  I have used C as the number of cookies, and n as the number of students in the room.  Now that you know the equations, you can substitute 9n+1 for C in the second equation to get {{{10n = (9n + 1) + 13}}}.  To solve, first add like terms to get {{{10n = 9n + 14}}}. Then, move 9n over to get {{{1n = 14}}}.  There are 14 kids in the class.