you can't find one solution to this.
there are multiple solutions.
you would solve it as follows:
y = number of students
x = number of rows.
the number of students will be equal to the number of rows * 7 + 15.
your equation would be:
y = 7x + 15
you can set up a table and have x going up one at a time and you will get:
x y
1 22
2 29
3 36
4 43
5 50
etc.
what this means is that you can have any number of rows and still have the number of students exceeding the number of rows available by 15.
to find one solution, you would need some additional information that would help narrow it down, like total number of students is equal to 50.
then you can solve using the equation.,
the equation is:
y = 7x + 15
y = 50 make the equation become:
50 = 7x + 15
subtract 15 from both sides of this equation to get:
35 = 7x
divide both sides of this equation by 7 to get:
x = 5
you can also graph the equation to see that there are multiple solutions available unless you have additional information to help narrow it down.
the graph would look like:
the x-axis is the number of rows.
the y-axis is the number of students.