To add the fractions we first find the Least Common Denominator (LCD) for 10 and 14.

The LCD for 10 and 14 is 70 = 2*5*7

Next, we convert each fraction to an equivalent fraction using 70 as our new denominator:

9/10 = (7*9)/(7*10)  we multiply by 7 since we want to have 70 in the denominator (70/10 = 7)

3/14 = (5*3)/(5*10)  we multiply by 5 since we want to have 70 in the denominator (70/14 = 5)

Now solving:

9/10 - 3/14 

becomes solving 

(7*9)/70 - (5*3)/70 = 63/70 - 15/70 = (63-15)/70 = 48/70 = 24/35