Explanation:
a. (3 - 2/3) ÷ (4/3 x 7)
= [(3 x 3) / (1 x 3) - 2/3] ÷ 28/3
= (9/3 - 2/3) ÷ 28/3
= 7/3 x 3/28
= 21/84
= (21 x 1) / (21 x 4)
= 1/4
b. 2/3 ÷ 5/6 - 2/5
= 2/3 x 6/5 - 2/5
= 12/15 - 2/5
= (3 x 4) / (3 x 5) - 2/5
= 4/5 - 2/5
= 2/5
c. (- 3/4 + 1/2) ÷ (2/5 - 5/2)
= [- 3/4 + (1 x 12) / (2 x 2)] ÷ [(2 x 2) / (5 x 2) - (5 x 5) / (2 x 5)]
= (- 3/4 + 12/4) ÷ (4/10 - 25/10)
= 9/4 ÷ (- 21/10)
= 9/4 x - 10/21
= - 90/84
= (6 x - 15) / (6 x 14)
= - 15/14.
If you have any doubt, then you can ask me in the comments.