To work this out we need to use a common denominator to split each square into the same number of squares.
The smallest common denominator of 12 and 15 is 60, as both 12 and 15 are factors of 60.
To convert the first square, we need to multiply both top and bottom by 5 to get an equivalent of 10/60, and for the second square by 4 to get an equivalent of 8/60.
Therefore we have 18 squares of a total of 120.
18/120 = 3/20 = 0.15
Given this is not an answer, I imagine the question was asking for the tots shaded areas added together (of one square) which would be 18/60 = 3/10 = 0.3