Lagrange’s theorem specifies: Order of subgroup divides the order of a group order of a group= number of elements in a group = 15
L is a subgroup
L ⊆ G and L ≠ G
Divisor of 15 = 1, 3, 5, 15
L is at least 4, that is L ≥ 4
Therefore, The size of L is 5