so try to find a common denominator for 4 and 14. 4 x 7 = 28 and 14 x 2 is 28.
so then do 13 x 2 because you multiplied 14 and 2 to get 28, so do 13 x 2 and you get for that fraction 26/28 then because you already have the denominator you multiply 1 and 7. you get 7. so you get 26/28 - 7/28= 19/28