Multiply both sides by 3 to clear the fraction

(1)   

Multiply both sides by 6 to clear the fraction

(2)   

Use (2) to substitute 6M for C in (1):





(3)   

Use (3) to substitute 9M for L






So Maria is either 1 or 2

If Maria were only 1, then, substituting
M=1 in (2)   




But

So she can't be only 6.
So Maria must be 2

(4)   M=2

substituting M=2 in (2)   




Normally one is only 11 in the sixth grade, but
Clara could have failed a grade. So Maria is 2,
and Clara is 12.

Using (4) to substitute 2 for M in (3)







Liz is 18.

Edwin