Medium level fractions

Question 1

(12x)/4 - (3x)/8 = ?

Answer 1

times (12x)/4 by 2 in the top and bottom

24x/8 - 3x/8 = 21x/8

Question 2

10x/5 - 2x/3 = ?

Answer 2

10x/5 times by 3/3 and 2x/3 times by 5/5
30x/15 - 10x/15 = 20x/15
which simplifies to 4x/3

Question 3

20x/3 - 5x/4 = ?

Answer 3

20x/3 times by 4/4 and 5x/4 times by 3/3

80x/12 - 15x/12 = 65x/12