First, find the LCM (lowest common multiple) for denominators 14 and 6:
LCM of 14 and 6= 42
Then multiply the numerators by the same number that you multiplied each denominator to achieve the LCM:
15/42 + 7/42
Now solve! (and simplify)
15/42 + 7/42= 22/42
= 11/12
Hope this helps!