Answer :

The answer is 3! 

explanation; 3x10 equals 30. the difference is 27 years and 30-3=27!
L = 10M
27 = L - M

27 = 10M - M

27 = 9M

M = 3

L = 10M = 10(3) = 30

Lane is 30 years old
Mel is 3 years old