Let's assume
x is the age of 11th grade student
we are given
Rhonda conducts a survey of the ages of students in eleventh grade at her school.
On November 1, she finds the average age is 200 months.
and
She also finds that two-thirds of the students are within 6 months of the average age.
so, we can set up equation as

now, we can solve for x







So, the minimum age of 11th grade student is 197 months
So, the maximum age of 11th grade student is 203 months
now, we are given age is 18 years
we will change into months


So, first of these students turn 18 is

months...........Answer