So firstly, do the multiplications:

Next, we want to find the LCM, or lowest common multiple, between the 3 denominators. In this case, it is 24. Multiply 42/8 by 3/3, 35/6 by 4/4, and 10/12 by 2/2:

Now add up all the numerators together to get 286/24, which can be simplified to 143/12 when divided by 2 on the numerator and denominator.
In short, 143/12 is the answer.