Let the upper class limit be x and the lower class limit be y.
Class mark = 10 …[Given]
Class-mark = (Lower class limit + Upper class limit)/2
∴ 10 = (x + y)/2
∴ x + y = 20 …(i)
Class width = 6 … [Given]
Class width = Upper class limit – Lower class limit
∴ x – y = 6 …(ii)
Adding equations (i) and (ii),
x + y = 20
x – y = 6
2x = 26
∴ x = 13
Substituting x = 13 in equation (i),
13 + y = 20
∴ y = 20 – 13
∴ y = 7
∴ The required class is 7 – 13.