You have: [2-(5/3u)]/[7-(5/3u)] and to simplify it, you must apply the steps below:
1. The common denominator is 3u, then:
(2(3u)-5/3u)/(7(3u)-5)/3u)
(6u-5/3u)/(21u-5/3u)
2. Then, when you multiply them, you obtain:
(6u-5)(3u)/(3u)(21u-15)
(18u²-15u)/(63u²-15u)
3. Factor the common term 3u:
3u(6u-5)/3u(21u-5)
4. Then, divide 3u/3u:
3u/3u=1
5. Finally, you have:
(6u-5)/(21u-5)